To examine whether mental process in female subjects is influenced by monthly sexual cycle. Reaction time (RT) was measured in twenty healthy female undergraduates, who had regular menstrual cycle, normal body mass index and normal hearing function, low anxiety level, and had no color blindness. Simple and choice RT to visual and auditory stimuli were measured using a response velocity measurement device. The RT measurements were done in day 4 of the cycle (menstruation phase) and day 7 (follicular phase) with the randomly assigned time order. Data were analyzed using paired t-test. Visual RT, auditory RT, and choice RT decreased significantly in follicular phase than during menstruation (p < 0.05). Mental process in female subjects is influenced by monthly sexual cycle