Leptin is 16 KD, a protein that is synthesized by adipose tissue, and it is involved in the 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 and of those 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 a reduction in 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 if may also act as the signal to the reproductive system that sufficient body fat exists to support a successful conception and pregnancy. Lindersson et al (1998) reported QTL for milk production traits close to the leptin gene (82.8 cm). Liefers et al. (2002) reported that heifers with the sau3IA – AB genotype produce 1.32 kg/d more milk and consume 0.73 kg/2 more food compared with the sau3AI - AA genotype. They suggested that RFLP – B alleles could yield a higher milk production without negatively affecting energy balance and fertility. The aim of this study is to estimate the frequency of the leptin gene in Brown Swiss cows and the relationship between polymorphisms at the bovine leptin gene locus with variation in milk production and reproduction traits.