The purpose of this study was to reexamine the friendship function structure of university students with respect to the closest same-sex friend, and investigate the relations between the friendship function and the loneliness. Loneliness Scale by Ochiai (LSO) was used for the loneliness measurement. As a result, factor analysis revealed six factors in the friendship function scale. Also, a path analyse indicated that there were sex differences in the friendship function related to the closest same-sex friend (who exerts an influence with respect to 'feelings of loneliness leading to increased isolation'). Furthermore, there was no relation between the friendship function and 'feelings of loneliness inducing a sense of individuality'. These results suggested that the friendship function of university students with respect to the closest same-sex friend have the different influence on the subscales of the loneliness.