Background: Professional socialization of nurses defines a process in which novice practitioners are trained to develop the attitude and skills to become professional practitioners. This study was conducted to assess the level of professional socialization among clinical nurses. Methods: This is a descriptive cross-sectional study. A total of 600 nurses from Tehran and Shahrekord teaching hospitals and Oil Company hospital in Abadan, were recruited through convenience sampling method, participated in this study. Data collection was based on a valid and reliable questionnaire consisting of two parts including demographic form and "Nurses' Professional Socialization" (NPS). Sta tistical analysis was carried out by Kruskal-Wallis test and chi-square tests using SPSS software, version 17 and P < 0.05 was considered statistically significant. Results: The mean score of nurses' professional socialization level was 213.96 ± 20.89. Nurses were at competent, proficient and expert levels with no novice or advanced beginner nurses. In professional socialization domains, there was a significant difference in professional autonomy, commitment and group participation among Tehran, Shahrekord and Abadan (p=0.001). There was a significant relationships between work experiences and group participation domain (χ 2 = 9.1, df = 2, P = 0.01) and also the total score of professional socialization (χ 2 = 6.8, df = 2, P = 0.03). Conclusion: Nurses in this study were highly and professionally socialized. It is important for hospital nursing managers to maintain and promote levels of professional socialization and help the new comers' resocialization process after their educational period.