A BSTRACT Aims: Unprofessionalism in the use of Facebook has been found among healthcare professionals including dental students. The improper content may be shared to the public, negatively impacting their professions. This study explored account privacy and professionalism on Facebook usage in conjunction with evaluating whether there were correlations among presence of clinical experience, account privacy, and professionalism. Materials and Methods: This study retrospectively explored professionalism in the use of Facebook among Mahidol dental undergraduates in the academic year 2019. The students who had identifiable Facebook and accepted a friend request were included into this study. The content on both “About” and “Wall” sections was examined and analyzed using descriptive statistics and χ 2 test. Results: Facebook profiles of 522 students were identified. There were 382 (73.18%) students who accepted the friend requests, revealing account privacy: 32 (8.38%) private, 200 (52.36%) limited, and 150 (39.27%) public profiles. Clearly unprofessional content was mostly relevant to sharing information of patients (15.97%), followed by parody content of patients (8.9%). Questionably unprofessional misconducts included political discriminations (14.66%), profanity (3.14%), and alcohol consumption (2.88%). Professionalism was found to be significantly correlated with privacy ( p <0.001) and clinical experience ( p <0.001). Conclusion: Unprofessionalism tended to be higher in clinical years, so professionalism should be emphasized constantly throughout the dental program, especially before starting clinical practice. Privacy concerns should also be suggested for students at the beginning of the program.