Introduction: Removable dentures should be resistant to chemical disinfection and temperature changes. Objective: Evaluate the effect of thermal aging and chemical disinfection on microhardness and flexural strength of resins. Materials and methods: Two flexible resins - Deflex® ClassicSR and Deflex®SupraSF and one thermo-polymerizable resin - ProBase® Hot were subjected to 1000 cycles of thermal aging (n=32) and three types of chemical disinfection (n=8): Corega®Whitening, Corega®Oxygen-Bio-Active, 2,5% Sodium Hypochlorite and control (distilled water). The Knoop microhardness and flexural strength at 3 points were evaluated. We used Mann-Whitney and T-tes (α = 0.05). Results: Thermal aging only influenced the microhardness of ClassicSR and SupraSF (p0.001). The microhardness values were influenced by the chemical disinfection in Probase®Hot (Corega®Whitening vs Control, Bleach and Sodium Hypochlorite) (p0,05), in ClassicSR (Bio-active vs Control; Corega®Whitening vs Sodium Hypochlorite) (p0,001) and SupraSF (Corega®Whitening vs Sodium Hypochlorite) (p=0,025). The flexural strength was influenced by chemical disinfection in SupraSF (Corega®Whitening vs Bio-active and Corega®Whitening vs Sodium Hypochlorite) (p0,05). Discussion: Disinfectant solutions affected the microhardness of all resins under study and the flexural strength of Supra SF resin alone. Thermal aging affects only the microhardness of the flexible resins. Conclusion: Chemical disinfection promoted significant changes in all resins and further studies are needed to determine the long term effect of thermal aging and chemical disinfection. Clinical Implications: Disinfectant solutions should be used with caution in order to preserve the physical and mechanical properties of the resins. Keywords: flexible resins, thermal aging, chemical disinfection, microhardness, flexural strength