The term sociosexuality is used to describe individual differences in people’s willingness to engage in uncommitted sexual relationships. The authors developed the revised Sociosexual Orientation Inventory in Japanese (SOI-J) to assess sociosexuality. In addition, we examined the effect of sociosexuality on flirting behaviors. In study 1 and study 2, we translated the revised Sociosexual Orientation Inventory into Japanese and confirmed its reliability and validity. The results of study 3 showed that male sociosexuality had an effect on male and female flirting behaviors. On the other hand, the results showed that female sociosexuality had no effect on male and female flirting behaviors. These results suggest that relationship initiation is controlled by females.