Nursing is a practice-oriented profession, and the goal of education is to cultivate confidence and assertiveness for future clinical practice. Nurturing a professional self-concept at school is expecting to help students to approach their success in the nursing profession. Using a hierarchical model associated with critical thinking, academic achievement, class climate, and work experience, this longitudinal correlational study explored the growth trajectory of professional self-concept over two years in students attending 2- or 4-year baccalaureate nursing programs. This was a longitudinal and correlational study with five repeated measurements. Questionnaire data were collected by using the Chinese version of the Nurses Self-Concept Instrument (NSCI-C) and the California Critical Thinking Disposition Inventory (CCTDI). Scores for overall professional self-concept ranged from 84.51 (standard deviation SD 12.34) when the students began this study to 89.28 (SD 11.23) at graduation. Hierarchical linear modeling yielded the growth trajectory of professional self-concept was significantly associated with time (β = 0.93, p < .01), CCTIDI (β = 0.13, p < .001), and class climate (β = 5.20, p < .01). An intraclass correlation coefficient was 55.48%. This study confirmed the positive growth trajectory of the professional self-concept in the nursing students' two academic years. The continuous development of the professional self-concept of nursing students is encouraged. Development of critical thinking through their studies, feelings of belonging in their classes, and campus culture all contributed to this trend. To construct a comprehensive hierarchical model, future investigations should use large sample sizes from various classes and conduct multisite evaluations. •The positive growth trajectory of the professional self-concept was found in the baccalaureate nursing students.•In the two academic years, the students’ overall professional self-concept was initially low and varied but grew gradually.•The students had a higher score of the leadership self-concept in the beginning and at the end of the study.•The professional self-concept was associated with students own affective dispositions toward critical thinking and class.