Objective: This study evaluated the effects of carbamide peroxide and hydrogen peroxide on the biaxial flexural strength and flexural modulus of bovine dentin. Materials and Methods: Thirty coronal dentin disks (0.5 mm thick × 6.0 mm diameter) were prepared from bovine teeth. The disks were randomly divided into three groups (n=10): A control group (unbleached), a group bleached with 10% carbamide peroxide (8 h at 37°C), and a group bleached with 38% hydrogen peroxide (three 10 min applications at 37°C). The specimens were tested in a biaxial flexural apparatus held in a universal testing machine at 1.27 mm/min until failure occurred, and the biaxial mechanical properties were calculated. For each test parameter, the data were statistically analyzed by Fisher's PLSD test (predetermined a = 0.05). Results: The group bleached with 38% hydrogen peroxide demonstrated significantly lower flexural strength than the unbleached control group. Hydrogen peroxide treatment resulted in a significantly lower flexural modulus compared with the control group and with carbamide peroxide bleaching. Conclusion: Exposure of dentin to hydrogen peroxide significantly reduced both the flexural strength and the flexural modulus compared with the no-treatment control, whereas exposure to carbamide peroxide did not significantly affect either parameter.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação Amparo à Pesquisa Estado de São Paulo (FAPESP)Universidade Estadual Paulista Júlio de Mesquita Filho, Departamento de Odontologia Restauradora, Faculdade de Odontologia de Araçatuba, Aracatuba, Rua José Bonifácio, 1193, Vila Mendonça, CEP 16015-050, SP, BrasilUniversidade Estadual Paulista Júlio de Mesquita Filho, Departamento de Odontologia Restauradora, Faculdade de Odontologia de Araçatuba, Aracatuba, Rua José Bonifácio, 1193, Vila Mendonça, CEP 16015-050, SP, BrasilCAPES: 3110/2010CNPq: 305777/2010-6