BACKGROUND Being a nurse is more than just a series of business activities and skills. In fact, it is a part of the process of socialization, which is internalization and development of professional identity. Professional socialization is necessary for involving the students in professional practices. Thus, the purpose of this qualitative research was to increase the understanding of professional socialization in nursing and explore the related factors from the perspective of registered nurses and nursing students. METHODS In this qualitative design, data were collected on 43 nurses with a variety of experiences using semi-structured interviews and focus groups in the Shiraz University of Medical Sciences in 2012. Data were analyzed through inductive content analysis. RESULTS THE DATA ANALYSIS REVEALED TWO MAIN CATEGORIES: (1) sense of belonging with three sub-categories of theory-practice incongruence, educational experiences and tacit knowledge and (2) forming professional identity consisting of three sub-categories of relatedness, internal motivation and role model. CONCLUSIONS This study demonstrates that in nursing, sense of belonging and professional identity contributes to professional socialization; it is suggested that these factors, which improve socialization in nurses, be taken into account by authorities.