The present study was undertaken to investigate differences between Japanese and United States undergraduates in the judgment of socially appropriate behavior, i.e., the strength of social norm. Both the Japanese scale of social norms and its English translation had 46 statements of behavior which were supposed to be socially appropriate both in Japanese and United States public or semi-public spaces. Subjects were asked to evaluate the degree of their agreement or disagreement with each statement on a five-point scale. "Tokushima" sample of Japan consisted of 156 undergraduates. There were two United States samples. "Irvine" sample consisted of 153 undergraduates while "Boulder" sample had 91 undergraduates. "Tokushima" sample was compared with the two United States samples by means of two-tailed t-tests. The findings of this study generally indicate that an overwhelming majority of social norms are stronger in Japanese undergraduates than in United States counterparts.