Dental resin-based composites (RBCs) have been widely used in dental treatment because of their excellent characteristics such as aesthetic, mechanical and biocompatibility properties. The aim of this study was to evaluate the effect of different composition of natural hydroxyapatite (NHAp) and silica as a filler in dental resin. Different ratio of silica (0, 5, 15, 20 wt%) was added to NHAp and mixed with organic resin. The resin used were bisphenol A glycidyl methacrylate (BisGMA)/triethylene glycol dimethacrylate (TEGDMA)/hydroxyethyl methacrylate (HEMA) with their ratio of 50/25/25 wt% respectively. The ratio of fillers and organic resins were 70:30 wt%. The composites were inserted into the mould and cured for 60 s on both sides. The surface roughness, Vickers hardness, flexural and compressive strength were evaluated and compared. The results indicated that the mechanical properties depending on the composition ratio of HAp and silica. The optimum composition with the highest flexural and compressive strength was 85 wt% of HAp and 15 wt% of silica. This result was met the standard requirement of dental composite.