There are only three female characters in Heart of Darkness of any note: Marlow's aunt, Kurtz's mistress/concubine, and Kurtz's fiance. It would not be unfair to describe the role of all as negligible; in literary terms, they all could be classified as 'flat' characters.
The novella's view of women, as expressed by Marlow, is a hybrid of late-Victorian hypocrisy, repression, and condescension combined with the blunt indifference and ignorance of one who, like Conrad, has spent much of his life in the harshly masculine world of seafaring. This perspective is encapsulated in the following passage, which demonstrates that he is 'at sea,' in more ways than one.
It's queer how out of touch with truth women are. They live a world of their own, and there had never been anything like it, and never can be. It is too beautiful altogether, and if they were to set it up, it would go to pieces before the first sunset. Some confounded fact we men have been living contentedly with ever since the day of creation would start up and knock the whole thing over.
Kurtz's native mistress, a "wild and gorgeous apparition of a woman," who Marlow first observes as she strides out proudly bedecked in brass leggings, gauntlets, and multiple glass-bead necklaces when he arrives to pick up the dismissed potentate, functions blatantly as a fetish object or totem. Like the resources of the land she inhabits, she is a prize of imperialist exploitation.
Marlow's aunt and Kurtz's "intended," as different as they are, are alike in their conformity to the Victorian stereotype of woman as a sheltered creature, dutiful in the domestic sphere, and without independent intelligence or initiative. They exist only as subordinates of men. When Marlow's aunt (who has gotten him the riverboat job) makes him "quite uncomfortable," by praising the Company's putative missionary efforts to "wean those ignorant millions from their horrid ways," he hints that a profit motive might be involved.
As feminist scholar Johanna M. Smith describes this type of exchange,
By mocking the lack of worldly experience which [her] words convey, [the narrator] can recuperate that experience as a manly encounter with the truth. To an even greater degree, this chasm of knowledge between Marlow and Kurtz's "intended," who seems utterly incapable of imagining what he has done or who he has become, renders her an inert, powerless non-person.
Is Conrad, then, a misogynist? If one judges his beliefs by Victorian standards, they are completely conventional, as we have seen. By the standard of the twenty-first century, however, it is clear they are highly misogynistic.