Materials & Method: This is  a cross- sectional study that was done on an accidental sample of 130 staff working in Shiraz University of  Medical Sciences (SUMS). The required data was gathered by using a questionnaire and descriptive statistics and person regression test were applied in significant level of 0.05.

 Results: Results showed that there were statistically positive significant differences   between OCB and organizational culture, personality and internal control focus (p<0.001) in contrast with the reversed and significant differences between OCB and job stress (p<0.001).In addition there were statistically positive significant differences   between various dimensions of OCB with each other (p<0.001). furthermore , between courtesy  and organizational culture, control focus and personality, citizenship behavior and organizational culture, sacrifice with culture and personality and between conscience and culture, the statistically positive significant differences   were observed in spite of the statistically negative significant differences between courtesy, citizenship behavior,  conscience with job stress and also between  conscience and personality(p<0.05).

Conclusion: reducing job stress , existing organizational justice and the group oriented organizational culture and also staff` characteristics the same as personality , control focus, etc can have an effective role on the incidence rate of Organizational Citizenship Behavior shown by staff in Shiraz University of  Medical Sciences . So attention to each of these dimensions and key factors and attempts for amplifying and supporting them by managers can develop these behaviors and lead to functional improvement in the organizations.