Social capital is one of the key concepts in the success of employees and organizations in the third millennium. This study aimed to investigate whether there was a meaningful relation between social capital and different dimensions of organizational citizenship behavior (OCB) including helpful behavior, magnanimity, loyalty, obedience, self initiative, civil behavior, and self development. The study followed a descriptive and statistical method. The data for the present study was gathered through library research and using standard OCB questionnaire and social capital questionnaire. The findings of the research indicated that there was a direct relation between social capital and organizational citizenship behavior among employees of Mashhad Municipality.