This study focuses on the gender problem and the emergence of the feminist science fiction through Joanna Russ’s The Female Man and Ursula Le Guin’s The Left Hand of Darkness. Traditionally, science fiction was considered as a masculine genre because the writers and reading audience were mostly men. Furthermore, the stories centered around male heroes and women hardly found any significant appearances when science fiction first appeared. Feminist science fiction was first seen in the 1970s. It explores gender discrimination and critiques the dominance of male power and institutions. The Female Man is about four women who lived in different times and spaces. When they cross over to each others’ worlds, their dissimilar views on gender roles startle the others’ pre-existing notions of womanhood. In The Left Hand of Darkness, Gethen adopt sexual attributes only during the period of sexual receptiveness and high fertility, called kemmer, in which individuals can assume male or female attributes, depending on the context and relationship. Russ’ and Le Guin’s text are responses to the radical currents within American feminism in the late 1960s. They directly confront the question of socialized versus biological differences and extends the fluid concept of gender.