In this study, friendship motivation scale was developed in the framework of the self-determination theory, and its reliability and validity examined. Following previous studies, we expected four subscales: external, internalized, identified, and intrinsic reasons. Validity of the scale was examined through confirmatory factor analysis, intercorrelations among subscales, and their correlations with other scales. Alpha coefficients and test-retest correlations were calculated to study the reliability of the scale. Also, the relationship between friendship motivation and prosocial behavior toward friends was examined. Results showed that the degree of self-determined motivation predicted the amount of prosocial behavior, and the relation between motivation and prosocial behavior was stronger in men than women. These results showed that the friendship motivation scale had sufficient reliability and validity, and its score was able to predict prosocial behavior toward friends.

Key words: friendship motivation, the self-determination theory, validity, reliability, prosocial behavior