The present study was to examine the relationships between motives for prosocial behaviors and internal-external locus of controls. Rotter's Internal-External scale was administered to 269 male and female university students. A factor analysis of 23 items indicated there were different aspects of internal-external locus of control, and two subscales (Loc I and Loc II) were constructed. Subjects, male and female students, were divided into Internals and Externals based on their subscale scores below or above the median of 190. They were then asked to rate the likelihood of 25 different helping motives as a cause of different 7 prosocial behaviors. Major findings obtained were as follows:(1) Internals of both Loc I and Loc II tended to attribute the prosocial behaviors to higher motives than Externals did, though the pattern of relationships was different between Loc I and Loc II.(2) The pattern of relationships varied according to types of prosocial behaviors and sex. The result suggests that the pattern of effects of internalexternal locus of controls on the motivational process in prosocial behavior depends on the situation.