Leptin is a 16 Kilo Dalton protein that is synthesised by adipose tissue and it is involved in regulation of feed intake energy balance, fertility and immune function. In cattle, the leptin gene is located on chromosome 4. It consists of 3 exons and 2 introns that only 2 exons translate into protein. Leptin treatment of animals has been shown to cause a decrease in food intake, body weight loss, fat depot weight loss and increase in energy metabolism therefore leptin not only causes reduced food intake but the potential body weight losses are enhanced due to an increased metabolic rate. Leptin may be involved in regulating reproduction in that it may also act as the signal to the reproductive system that sufficient body fat exists to support a successful conception and pregnancy (Fruhbeck et al., 1998). Lagonigro et al. (2003) reported association of five SNP bovine leptin genes with feed intake and fat–related traits. Liefers et al. (2002) reported that heifers with the AB genotype produced 1.32 kg/d more milk and consume 0.73 kg which is 2 times more food compared with the AA genotype. They suggested that B allele could yield a higher milk production without negatively affecting energy balance and fertility. The aim of this study was to estimate the frequency of the leptin gene and its relationship between its polymorphisms with variations in growth and age at successful insemination in an Iranian native cattle, Sistani.