Purpose: This descriptive study was done to identify effects of perceived organizational support (POS) on job involvement and organizational citizenship behavior (OCB) in hospital nurses. Methods: Data were collected from Oct. 1 to Nov. 15, 2011. Participants in this study were 324 nurses working in 6 general hospitals in S, K, and C cities. Data were analyzed using descriptive statistics, t-test, ANOVA, Scheffˊe test, Pearson correlation coefficients, and multiple regression. Results: POS was positively correlated with job involvement, and OCB (altruism, conscientiousness, courtesy, sportsmanship and civic virtue). Factors influencing job involvement were POS and marital status, which accounted for 15.7% of the variance, marital status influenced altruism, which accounted for 4% of the variance, POS influenced conscientiousness, which accounted for 10% of the variance, religion and marital status influenced courtesy, which accounted for 6.5% of the variance, age influenced sportsmanship, which accounted for 7.9% of the variance, and POS and clinical career influenced civic virtue, which accounted for 23.1% of the variance. Job involvement mediated on the relation between perceived organizational support and organizational citizenship behavior. Conclusion: The results of the study indicate that hospital administrators should explore ways of improve POS for better job involvement, conscientiousness, and civic virtue.