Abstract : This randomized controlled clinical trial is aimed to evaluate the clinical performance of high viscosity bulk fill resin composite and compomer in the restoration of second mandibular primary molars compared to conventional incremental resin composite. The studied sample consisted of 60 second mandibular primary molars in 59 children aged between 5-8 years, these cases were allocated randomly into three groups: Group 1 (experimental, n=20): High Viscosity Bulk Fill Resin composite (HVBFC), Group 1 (experimental, n=20): Compomer, and Group 2 (control n=20): Conventional Incremental Resin composite (CIC). Post-treatment clinical follow-ups were conducted during 3, 6, and 12 months using Modified United States Primary Healthcare Service (USPHS) criteria. Data were analyzed using Kruskal- Wallis test. The clinical success rate reached 100%, 95%, and 95% in HVBFC, Compomer, and TIC groups respectively. Statistical analysis revealed no statistically significant differences among HVBFC, Compomer, and TIC groups in overall clinical evaluation (P-value= 0.375). Bulk fill resin composite, compomer, and conventional resin composite restorations showed satisfactory clinical performance in primary molars during the 12-month follow-up period.