Toxoplasmosis is a zoonotic disease caused by an intracellular protozoan of  Toxoplasmagondii, that has not been examined in Lorestan yet; this study aimed at the prevalence rate of IgG in the domestic ruminants, based on the variable factores of species, sex and Geographic region. Therefore, from October toFebruary 2012, 572 blood samples (174 Cattles and 398 sheep) were collected from the slaughterhouses of Khoramabad, Boroujerd and Aligoudarz. The serum samples of sheep, were examined by indirect ELISA method, and the result was calculated based on the ratio of the absorbancevalues of the samples to the positivecontrol, so that ≤30% as negative, and ≥50% was considered as positive.The Cattle serum samples,were examined via Indirect Immunoflourecence antibody test, and the Titer ≥ 1:16 was considered as positive. In this study, the IgG prevalence rate in cattles and sheep was 28.73% and 53.01% respectively, and the statistic analysis of the results, demonstrated that based on the sex and species, there was a considerable statistic difference, so the lowest infection rate was observed in cattle, and the most infection rate was observed in the sheep, The prevalence rate in females was higher than that in males but there was no significant difference geographically (P