Toxoplasma gondii is an obligate intracellular coccidian parasite that can infect virtually all species of warm-blooded animals and humans. Domestic cats and other Felidae are the definitive hosts. All non feline hosts are intermediate hosts. The importance of this parasite is due to the fact that it causes congenital toxoplasmosis, abortion and mortality in both human and animals. Toxoplasmosis is a major cause of death among patients with AIDS. The efficacy of Clindamycin and Monensin were evaluated in the prevention of oocyst shedding of kittens with Toxoplasma gondii (Tehran strain). In this study 28 healthy kittens aged 1.5 - 2 months old divided randomly into 4 groups of seven. In group 1, that fed infected brain tissues of mice, all of seven kittens (100 %), shed oocyst, nearly 1 week after infection, which lasted for 8 to 9 days. In group 2, which fed infected brain tissues of mice and Clindamycin at dose of 20 mg/kg from day -3 to + 21 after infections, none of seven kittens, shed any oocyst. In group 3, that fed Clindamycin at dose of 10 mg/kg, same as group 2, two of 7 kittens (28/6%), began to shed oocyst from day 11 to 18 after infection. Kittens of group 4 that fed Monensin at dose of 0.02% incorporated in dry food didn't shed any oocyst. Data analysis revealed that Clindamycin 20mg/kg and Monensin 0.02% had a 100% inhibitory effect against Toxoplasma gondii (Tehran strain). No adverse reactions were observed during the experimental period.