Feminism is a movement which insists women should have rights equal to men--social, economic, and political rights are all included. Several feminist female writers--Margaret Atwood, Virginia Woolf, George Eliot (Mary Anne Evans) and others--experienced great success with literature focused on this movement.
Gender studies is broader and analyzes both the feminine and masculine, sexuality, and factors which affect these (geographical location, race, culture, etc.). Gender studies explores the distinction between socially-acceptable roles for men and women, but also includes a psychological aspect of analysis in determining the nature of these roles. Most conversations in gender studies revolve around the aspect of power within gender, as well as within the traditional and nontraditional roles which define human beings. However, some critics feel that gender studies is directed more toward an examination of women, rather than men.