Objective: To evaluate the efficacy of a disinfectant based on hydrogen peroxide. Methods:The method used to assess the efficacy of the disinfectant was the agar plate technique. With this procedure, it was possible to determine the percentage of inhibition of the high-level disinfectant of STERIS against four microorganisms, i.e., Pseudomonas aeruginosa ATCC 9027, Staphylococcus aureus (Beta-Hemolytic 227), Salmonella choleraesuis (Kuznedorf CMDM 074), and Bacillus subtilis (ATCC 6633). The effectiveness of five disinfectant concentrations (0.02%, 0.04%, 0.08%, 1%, and 2%) was determined and evaluated in three different times 5, 10, and 15 min, for vegetative strains and 3, 6, and 9 h for the sporulated strain. Results:According to the experimental test, the reduction of the microbial population was, on average, 100% for the disinfectant concentrations of 0.08%, 1%, and 2%. Conclusion:The results obtained demonstrated that the high-level disinfectant of STERIS based on hydrogen peroxide is 100% effective when the concentration recommended by the commercial house (2%) is used in the shortest time exposure to disinfectant. The minimum level of effectiveness was 0.08%; however, if lower concentrations are used, destruction of the microorganisms is not guaranteed.