BACKGROUND: Blended learning is being integrated into undergraduate nursing education at all levels and from all directions. Cognitive engagement is not only an embodiment and guarantee of students' engagement into the curriculum from a cognitive level, deep engagement and high-level thinking, but also an important indicator of whether students are effectively engaged in the blended learning curricula. However, no studies have been seen to investigate the cognitive engagement of nursing undergraduates in the blended learning curricula and its influential factors. OBJECTIVES: To explore nursing undergraduates' cognitive engagement during the blended learning curricula and its influential factors. DESIGN: A convergent parallel mixed-methods was used. Data were collected between November 2021 and May 2022, inclusive. SETTINGS AND PARTICIPANTS: The study was carried out in the nursing school at a university in China. Participants including students undertaking entry to the blended learning curricula. METHODS: In the quantitative component (n = 142), participants' cognitive engagement was investigated and factors associated with it were examined using univariate analysis, correlation analysis and multiple regression analysis. During this period, personal, semi-structured interviews were conducted with a subset of these participants (n = 15) to understand participants' cognitive engagement experiences. RESULTS: The cognitive engagement of nursing undergraduates was at a moderate level and the cognitive engagement experiences were reflected in the four themes of Reconstitution, Connection, Elaboration and Retention. The influential factors of cognitive engagement were learning activities (ß = 0.226, p = 0.004), autonomy (ß = 0.158, p = 0.047), academic self-efficacy (ß = 0.311, p < 0.001, ß = 0.271, p < 0.001) and social interaction (ß = 0.358, p < 0.001). CONCLUSIONS: The cognitive engagement of nursing undergraduates in the blended learning curricula needs to be improved. To maximize promote cognitive engagement of nursing undergraduates in the blended learning curricula, educators should design diverse learning activities, engage in high quality social interactions with students, and maximize students' autonomy and self-efficacy.