The present study integrated social exchange theory and motivational perspective to explore the mediating role of felt obligation and boundary condition of personal motives in the relationship between psychological contract fulfillments (PCF) and organizational citizenship behaviors (OCB). We hypothesized that (a) PCF exerts influences on OCB through felt obligation; (b) the PCF-OCB relationship would be stronger when employees are high in altruistic and high in egoistic motive. Accordingly, an integrative model of exchange theory and motivational theory would be proposed to simultaneously examine the mediated effect and interactive effect on organizational citizenship behaviors. We tested the hypothesized model by using data of supervisor-subordinate dyads. Data are collected through employees¡¦ self-reports and employees¡¦ supervisors, so two questionnaires are use. Obtaining measures of the predictor and criterion variables from different source is one of the procedures used to control common method bias, a critical limitation in cross-sectional correlational research (Podsakoff, MacKenzie, and Lee, 2003). A sample of 485 supervisor-subordinate dyad was obtained from supervisory MBA graduates and their randomly-selected subordinates. All survey measures process the back translation procedure recommended by Brislin (1980) to assure the equivalence before administration. Confirmatory factor analysis is employed to examine the psychometric properties of all measures used. Finally, to test hypotheses, structure equation modeling using statistical package Liseral 8.5 and hierarchical moderated regression were employed. Resulted showed that social exchange theory and motives significantly explained the PCF-OCB association in different way, as we expected. First, we found that felt obligation is influenced by balance and relational PCF and then in turn has impact on etic OCB, while transactional PCF had no effects on either felt obligation or two forms of OCBs. Additionally, results strongly suggested that the negative effect of transactional PCF on OCB occurred for people low in altruistic motive to help, but would be positive associated for people high in altruistic motive. The findings signify that altruistic motive interacted in such a way that a strong altruistic motive was needed to buffer the negative effect of transactional PCF on etic OCB. It¡¦s important to note that transactional PCF had no direct effect on any forms of OCB, thus it appeared that altruistic motive played a role of ¡§switch¡¨ to activate the relationship between transactional PCF and every forms of OCB. Finally, we found altruistic motive, instead of egoistic motive, is the key determinant for OCB.