Objective: To evaluate the effectiveness of an oral self-care education intervention based on the Theory of Planned Behavior in Taiwanese undergraduates. Participants: We recruited 63 and 90 students in the experimental group (EG) and comparison group (CG), respectively, from a medical university. Methods: A quasi-experimental design was employed. The EG received health education and a brief action and coping planning intervention. Results: The EG was significantly more likely to brush for more than 3 minutes (adjusted odds ratio [aOR] = 2.52), use the modified Bass brushing technique (aOR = 7.81), and floss (aOR = 21.21) at the 2-week follow-up than was the CG. At the 6-week follow-up, the combined effect of high action and coping planning with high perceived power for predicting floss use was observed in the EG (p < 0.05). Conclusions: Intervention may promote periodontal-disease-preventing behaviors in undergraduates, particularly for achieving adherence to daily flossing.