Purpose: Professional identity (PI) formation occurs over time through immersive social—digital and in-person—interactions. While digital social interactions may support the PI formation of medical students, their influence remains underexplored. This study aimed to describe the patterns and intensity of social media use and analyze its association with PI. Methods: This quantitative cross-sectional study was conducted at a private medical school in Jakarta, Indonesia. All undergraduate medical students were invited to participate in this study. Data were collected using the Social Networking Activity Intensity Scale (SNAIS) and the MacLeod Clark Professional Identity Scale (MCPIS-9) questionnaire. Data were analyzed descriptively and statistically. Results: A total of 451 students participated in this study. Participants reported moderate overall social media use intensity (mean SNAIS=2.96±0.51), with higher use for entertainment than social interaction. The mean MCPIS-9 score was 3.76±0.44. Content engagement, measured using a content engagement index (CEI) reflecting the intensity of engagement with educational and informational content across selected social media activities, was generally low and driven mainly by browsing behaviors (CEI=0.51±0.64). Weak but significant correlations were observed between CEI and MCPIS-9 (ρ=0.139, p=0.003) and between SNAIS and MCPIS-9 (r=0.102, p=0.030). One-way analysis of variance revealed significant differences in MCPIS-9 scores by duration of use for WhatsApp and X, but not for other platforms. Conclusion Participants mainly used social media for entertainment purposes. Social media use intensity and content engagement showed weak but significant associations with PI.