Belief bias in syllogistic reasoning occurs when individuals' agreement with a conclusion influences their assessment of its logical validity. While this effect has been widely studied in domains such as politics and personality-related reasoning, its role in evaluating arguments about sexual violence remains underexplored. In a pre-registered study, we examined whether participants' sexist beliefs and cognitive reflection influenced their ability to assess the validity of syllogisms related to sexual violence. Participants (N = 104) completed a syllogistic reasoning task with sexism-supportive, sexism-challenging, and neutral syllogisms, as well as the Ambivalent Sexism Inventory and a Cognitive Reflection Test. The results indicate that when evaluating such syllogisms, participants' beliefs play a significant role. People tend to perceive syllogisms as logically valid if the conclusions align with their beliefs and as logically invalid if the conclusions contradict their beliefs. Furthermore, cognitive reflection moderated belief bias effects, but only for sexism-supportive syllogisms. These findings highlight the extent to which reasoning about gender and sexual violence is shaped by preexisting beliefs and suggest that cognitive reflection may help mitigate some bias-driven reasoning errors.