Objective The purpose of this prospective randomized clinical study was to compare the clinical performance of thermo-viscous bulk-fill resin composite versus conventional bulk-fill resin composite in proximal compound posterior restorations. Materials and Methods: A total of fifty-four Class II cavities were prepared in forty-seven patients. The patients were divided into two groups according to the type of the bulk-fill used (n=27).Group 1 : thermo-viscous bulk fill (Viscalor,Voco) while Group 2: conventional bulk fill (Xtra-fil ,Voco). Both groups received the same adhesive system; selective enamel etching using the single dosed dual cured universal adhesive (Futura-bond U, Voco). All restorations were clinically evaluated at periods of 1 week (initial recall), after six months, and after one year. Assessment was done according to the modified United States Public Health Service (USPHS) criteria. Data were statistically analyzed using Friedman to compare between the tested periods for each group (p < 0.05). Results: There was no significant difference between group 1 and group 2 regarding all tested criteria at different follow up periods; where P > 0.05. Conclusions: Thermo-Viscous Bulk fill composite (Viscalor bulk fill) and conventional packable bulk fill composite resin (X-tra-fil) exhibited comparable acceptable clinical performance after one year of clinical evaluation.