The main purposes of this study were to explore factor structure of preschool teachers' organizational citizenship behavior (OCB) and correlation factors by using nested factor structure and hierarchical linear model. The data were collected through questionnaires from a sample of 395 preschool teachers at Kaohsiung County, Kaohsiung City and Pingtung County. Nested factor structure confirmatory factor analysis showed that measurement of OCB includes general and specific factors. And the amount of specific factor variance was more than general factors. Hierarchical linear models indicated there are significant and positive main effects of professional commitment and organizational trust on OCB.