Discriminant validity, dimensionality, convergent validity, and reliability of Griffin, Neal & Parker’s (2007) Proactive Behavior Scale were investigated in Japanese workplaces. In the first survey, 516 participants completed the scale. Confirmatory factor analyses indicated that the scale could discriminate proactivity from proficiency and adaptivity, and that proactivity consists of three dimensions: individual tasks, team membership, and organizational membership. Moreover, results of regression analysis indicated the convergent validity of the scale. Of the original sample, 312 respondents participated in the second survey conducted two months later. The coefficient alpha and test-retest reliability indicated sufficient internal consistency and acceptable stability of the subscales. Overall, the findings of this study confirmed the utility of the Proactive Performance Scale for use in the Japanese context.