Fats in the diet can influence reproduction positively by altering both ovarian follicle and corpus luteum (CL) function and by increasing precursors for the synthesis of reproductive hormones such as steroids and prostaglandins (Mattos et al., 2000). Fat supplementation positive effects include: increased size of the ovulatory follicle, increased numbers of ovarian follicles, increased plasma concentration of progesterone, reduced secretion of PGF2α, increased lifespan of the CL, and improved fertility (Staples et al., 1998). Lucy et al. (1992) suggested that it was fatty acids, and not the additional energy provided by the fatty acids, that stimulated ovarian function. Recently, new information has been published that demonstrates that the type of dietary fatty acids is important as individual fatty acids do not have the same effects on reproduction of the dairy cow (Petit et al., 2001).The objective of this study was to determine the effects of dietary supplemental fat source on reproduction parameters in Iranian fat-tailed ewes.