Targeting at high-tech industry, the major purpose of this study aimed to explore what kind of effect that transformational leadership and employees ' positive affectivity on employees' organizational citizenship behaviors. This study used dyadic questionnaires by collecting data both from managers and employees, and obtained 237 valid samples from the high-tech companies. By analyses of hierarchical regression , the study results showed that transformational leadership and employees' positive affectivity both have positive effects on employees' organizational citizenship behaviors , while employees ' positive affectivity moderated negatively on the relationship between transformational leadership and organizational citizenship behavior. The academy and management contribution and implications of this study are discussed and some suggestions for future research are recommended.