Abstract: Listeria monocytogenes is a facultative, intracellular, gram positive bacterium that is responsible for sever infections, including prenatal infections, septicemia and meningoencephalitis in humans and a wide variety of animal species. In this study, efficacies of co-trimazine in an immunosuppressed mouse model of listeriosis was compared with co-trimoxazole. After treatment with co-trimazine (400 mg kg-1 of sulphadiazine and 80 mg kg-1 of trimethoprim) every 12 h for 3 days, Listeria monocytogenes could not recovered from the livers of the mice. In contrast, after treatment with co-trimoxazole (400 mg kg-1 sulphamethoxazole and 80 mg of trimethoprim) every 12 h for 3 days, a mean of 3 x 103 colony-forming unit (CFU) was recovered from the livers of mice. Results showed that antibacterial efficacy of co-trimazine was more than co-trimoxazole in experimental infections with Listeria monocytogenes.