Abstract Background & Objectives: one of the most common problems in metal ceramic restorations is the loss of porcelain- metal bond that causes the treatment to fail. The aim of this study was to evaluate fracture mode of Ceramco and Noritake porcelains bonded to Commend base metal alloy after various surface treatments. Materials and Methods : In this laboratory study, 64 wax papers in size of 1 x 8 x 25 mm were cut with a surgical blade and after investing , burning out, casting with base metal alloy and surface treatment, were divided randomly into two groups. Porcelain application was done by Cermco porcelain in one group and by Noritake porcelain in the other. Surface treatment in each group was randomly accomplished by one of four different methods to improve metal-porcelain bonding. Porcelain fracture of the samples was evaluated by 3- point bending test by Universal Testing Machine with the speed of 1 mm per minute. Photos were taken from the samples. Results In the Ceramco porcelain group, the highest percent of cohesive failure was in the sandblast, grinding, sandblast, oxidation subgroup (22%) and in the Noritake porcelain group, it was in the sandblast , grinding, sandblast, steam cleaning , oxidation subgroup (96.97%)( P value<0.001). Conclusion: Performance of oxidation stage increases the percent of cohesive failures. Type of applied porcelain is effective on percent of cohesive failure without considering type of surface treatment and Noritake porcelain showed more failure.