Objective: to analyze the process of professional identity construction in undergraduate nursing students during their education. Method: qualitative research, anchored in the Historical-Cultural framework. Twenty-three undergraduate nursing students took part. Data were collected through individual interviews, with a semi-structured script. Thematic Analysis was used to analyze the data. Results: the following four themes were obtained, “The subject in movement to become a nurse: from previous experiences to entering the courses”; “The nursing professor in the construction of the undergraduate’s professional identity: a two-way mirror”; “Pedagogical relationship: instrument for constructing the student’s professional identity” and “Historical-cultural conditions: space for the construction of the student’s professional identity”. Conclusion: the construction of the students’ professional identity is limited to the material conditions of existence, translating appropriation to the intrapsychic scope of elements that occur, first, in the inter-psychological space of interactions. Nursing professors can become a paradoxical mirror, with one face to be imitated and the other, which materializes meanings of a model not to be followed. This construction is also influenced by the conditions of professional practice and university education.