The purpose of this study was to evaluate the effects of the silane coupling agent amount on the flexural properties and hydrolytic durability on an experimental composite resin for understanding the optimum amount of silanation. A spherical filler was silanated with 7 different amounts of γ-MPTS, 0, 0.17, 0.34, 0.66, 1.36, 2.72 and 5.45mass%. Photopolymerized experimental composite resins were made from a 70/30mass% of UDMA/TEGDMA and a 65mass% of different silanated amounts of filler. Bar-shaped specimens were prepared for a 3-point bending test in 37°C water after 1-day water storage at 37°C and after an additional 1, 7, and 28 days hot water storage in Soxhlet's extractor. The flexural strength and flexural modulus of unsilanated filler dramatically decreased after 28 days hot water storage while those of silanated filler showed a slight change. These results suggested that the silanated amount on the silica filler is not sensitive for flexural properties and hydrolytic stability of composite resin.