A good thesis statement about good and evil from The Strange Case of Dr. Jekyll and Mr. Hyde is that good and evil are not distinct from each other but are intertwined and defined by each other. Dr. Jekyll, the quintessentially morally upright man in the eyes of society, has long contended with the secret darker side of himself. He writes a letter in which he explains his understanding of the dualistic nature of humans:

In his novel, The strange case of Dr Jekyll and Mr Hyde, Robert Louis Stevenson explores the duality of human nature - that man is, at once, both evil and good. In his characterization of Mr Hyde as Dr Jekyll's evil persona, he wishes to convey the intricate complexity faced by man: "What is my true nature, my true will? To exercise goodness and humility or to succumb to savage desire and degradation?"

Robert Louis Stevenson's The Strange Case of Dr. Jekyll and Mr. Hyde depicts a man torn between his "good" and "evil" self. This idea has been popularized in Gothic Romantic works (like Stevenson's text and Mary Shelley's Frankenstein). Gothic Romantic authors, when dealing with the doppelganger (a person's "twin"), play upon the idea that people possess both good and evil within themselves. While the amount of good and evil is unknown, everyone possesses the ability to be both good and evil. 

A thesis statement which addresses the idea of good and evil within the text is as follows.

The dual nature of human mentality, symbolized by the evil of Mr. Hyde and the good of Dr. Jekyll, illustrates the battle which rages within an individual. Robert Lewis Stevenson's The Strange Case of Dr. Jekyll and Mr. Hyde represents the battle between the intellectual and rational self and the irrational and animalistic self. 

What is a good thesis statement for The Strange Case of Dr. Jekyll and Mr. Hyde?  

A thesis statement needs to state an opinion: it needs to be arguable. Therefore, you wouldn't want to say that The Strange Case of Dr. Jekyll and Mr. Hyde is about a man who splits himself into two people or that it is set in London. These are facts that nobody can dispute.

A thesis statement also needs to be specific. Saying that Dr. Jekyll and Mr. Hyde is about evil maybe arguable, but it is too broad. A thesis statement also needs to be supportable: whatever it asserts has to be supported by quotes and events from the text.

With these ideas in mind, we can move to the novel. What message or messages is it trying to convey? An idea might be as follows: Dr. Jekyll believes that if he could separate out his evil desires and impulses, life would become more "bearable." Yet when he creates his Mr. Hyde or evil self, this evil person feels

younger, lighter, happier in body; within I was conscious of a heady recklessness ... an unknown but not an innocent freedom of the soul.

A thesis statement could argue that it is dangerous to try to become a wholly good person, because when we try to cut out or repress our evil impulses, they come back in a stronger way to haunt us, as Mr. Hyde does when he does terrible things that trouble Dr. Jekyll.

A thesis statement might say something like the following.

The Strange Case of Dr. Jekyll and Mr. Hyde shows that when our evil desires are separated from our consciences, these desires grow stronger and more dangerous.

You might then give examples showing that Mr. Hyde acts badly and that Dr. Jekyll is less free of his evil side than ever. Or you might want to think about the idea that evil is a very strong impulse and what the story is saying about this. Can humans ever escape evil? Is it better to try to integrate it?

What is a good thesis statement about The Strange Case of Dr. Jekyll and Mr. Hyde?

This novella explores what was largely uncharted territory in the late nineteenth century about scientific and medical research and experimentation, especially regarding human psychology. In the 130 years since its publication, similar stories have become entirely commonplace. An effective essay needs to address the most serious issues Robert Louis Stevenson grapples with, which have given the book staying power and even made the characters' names synonymous with diametrically opposed alter egos.

Among the issues to consider is the possibility of dual personalities coexisting within a person. Was Jekyll naturally evil as well as good? Did the experiments bring out what was already inside him? Or did they cause him to become evil and adopt another persona?

Today, medical review boards enforce stringent ethical guidelines. Perhaps the doctor was justified in experimenting on himself, but an essay about his ethics as related to the direct and indirect effects of his decisions could argue for or against his behavior.

What is a good thesis statement about The Strange Case of Dr. Jekyll and Mr. Hyde?

That depends on the assignment.  

Have you been given an assignment that involves a specific question about the book, or that points you in the direction of certain themes? Since you don't mention anything like that in your question, I'm going to assume you haven't been given any such thing, and have just been asked to write an essay or a paper about Dr. Jekyll and Mr. Hyde, with the topic left wide open. 

A thesis statement should be brief and clear, and it should make a claim about the book that it will take you the rest of the essay to prove.

Here are a few suggestions of possible thesis statements to get you started:

• "The process of disintegration that Dr. Jekyll goes through over the course of the novel resembles the process of drug addiction."
• "Although Utterson is a good person and a very good friend to Dr. Jekyll, he is unable to save Dr. Jekyll from himself."
• "The novel would have a very different effect on readers who do not know from the start that Dr. Jekyll and Mr. Hyde are the same person."
• "The author's many chilling descriptions of Hyde help us feel the horror of a person who is entirely without conscience."
• "Throughout the novel, Dr. Jekyll has experiences and feelings that all people can identify with."