The 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.