Although organizational citizenship behavior (OCB) can be regarded as a key factor of the sustainability of virtual communities, comparatively little research has been conducted on investigating antecedents of OCB in virtual communities. Our model posits that user evaluations such as utilitarian value, hedonic value and social value affect user involvement, which in turn, influences organizational citizenship behavior. Survey data from 534 respondents was used to test the model using partial least square analysis. Utilitarian value, hedonic value and social value were found to have significant impacts on OCB that were either partially or fully mediated by user involvement. The implications of these findings for both research and practice are discussed.