Deriving from social exchange theory and the concept of role definition, this study developed and tested a model of how contact employee perceptions of social support influence affective commitment, which contributes to their extra-role customer service behaviors. Dyad-data was collected from 198 contact employees and supervisors of 20 branches in Taiwan's largest hypermarket group and analyzed using structural equation modeling (SEM). The results reveal that organizational support and co-worker support have indirect effects on extra-role customer service behavior through affective commitment. In addition, co-worker support directly contributes to the exhibition of extra-role customer service behavior. Based on the findings, some managerial implications and suggestions for further research are proposed.