Socialization is a basic and fundamental concept in nursing. There is a great need to evaluate professional socialization of nursing students. The aim of study was determining the factors affecting on the level of professional socialization of nursing students in Ilam University of Medical Sciences in Iran. The design was cross-sectional and 130 nursing students of Ilam University of Medical Sciences in Iran were selected by convenience sampling. Data were gathered by socialization questionnaire of professional socialization and analyzed by t- test in SPSS17. Significance level was considered to be 0.05. The most of the students were male (63.1%), single (96.9%) with mean age of 21.11 ± 2.61 ranged 18-31 years. Mean score of socialization was 37.71 ± 8.48 with a minimum of 23 and a maximum of 51. Score of socialization were at novice (11.5%), advanced beginner (45.4%), competent (43.1%). None of them were not in proficient and expert levels. A statistically significant relationship was observed between mean score of socialization competence of the nursing students with age, education level and gender (p< 0.05) and between the mean score of socialization level of nursing students in all dimensions of the questionnaire except group participation (p< 0.05). The level of professional socialization in the most students was advanced beginner. Therefore it is necessary to promote professional socialization by proper intervention. The results can obtain the necessary data for studentsand educational planners for promoting the socialization level of students and identify the strengths and weaknesses of their educational planning and administration.