In the more than one decade, studies of organizational citizenship behavior(OCB) have increased continuously, research on the role of job satisfaction and organizational commitment upon the relationships between OCB and Job characteristics, however, is very scarce. This study analyzed comprehensively existing studies of OCB, designed a model of mediating role of behavioral performance(job satisfaction, organizational commitment), and generated three hypotheses inherent in the model. To design the model and generate the hypotheses, this study conducted a comprehensive literature survey on OCB. To test the hypotheses, this study collected data from 847 employees at 12 large general hospitals in Pusan area through a questionnaire survey and conducted the three step mediated regression analysis using the SAS-PC Package. Conclusively, job characteristics tend to be the most influential antecedents affecting not only through mediating factors but also directing to OCB. These and other major findings from this study imply that existing American studies may be applicable the Korean organizations and that this study may complement the deficiencies of the existing studies.