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Social discounting rates were compared between Japanese and American college students. In a series of psychophysical questionnaire tasks, participants chose between a hypothetical unshared monetary reward and a hypothetical monetary reward to be shared with other people (relatives or strangers), to determine amounts of the unshared reward subjectively equivalent to the shared reward. The participants also chose between sharing and not-sharing options in a one-shot dilemma game. Discount rates estimated by a hyperbolic function were higher among the Japanese students than among the American students. Moreover, the discount rates obtained in the relative condition were lower than in the stranger condition. In addition, participants who chose the sharing option in the dilemma situation showed lower discount rates. These results suggest that discount rates reflect a cultural difference as well as a degree of “selfishness.”