BackgroundIn response to the aging population, it is essential to examine gerontological service career adaptability among health science undergraduates. ObjectivesThis study aimed to clarify the trajectories and predictors of health science undergraduates' gerontological service career adaptability. DesignThis study adopted a longitudinal design. SettingsThis study was conducted at four universities in China. Participants and methodsHealth science undergraduates were recruited via convenience sampling. Data were collected in the third (Stage 1), sixth (Stage 2), and ninth (Stage 3) months of the participants' graduation year. A total of 471 undergraduates completed a three-stage self-report questionnaire that assessed gerontological service career adaptability, career motivation, proactive personality, and practice environment at Stage 1 and gerontological service career adaptability at Stages 2 and 3. The response rate was 76.84 %. Data analyses entailed multiple linear regression, a latent growth mixture model, and multiple logistic regression. ResultsThree subgroups representing different gerontological service career adaptability trajectories were identified: rapidly growing (6.16 %), stably growing (87.47 %), and decreasing (6.37 %). Changes were observed primarily from the third to sixth months of the participants' graduation year. Health science undergraduates with high career motivation and a strongly proactive personality were likely to be in the decreasing group, whereas those with a supportive practice environment were predisposed to belong to the decreasing and stably growing groups. ConclusionsThe health science undergraduates' gerontological service career adaptability trajectories are heterogeneous, with the critical period spanning the third to sixth months of their graduation year. Gerontological service career adaptability grows stably among most undergraduates who have a supportive practice environment. Additionally, gerontological service career adaptability changes easily among undergraduates with high career motivation and a strongly proactive personality. Educators should implement tailored interventions to enhance gerontological service career adaptability based on health science undergraduates' traits.