Abstract: The objective of this study was to consider the genetic variations in the exonII region of the leptin gene for the Iranian Holstein cows. Association between leptin genotype with milk production and reproductive traits were analyzed by a univariate linear model. Result is shown that the T allele had significant effect on milk yield versus C allele. This effect was severe particularly for cows which had 60 and 100 milking days (p<0.028). Homozygous animals for the TT genotype produced more milk (1.6 kg day-1) than CC animals. However the association analysis showed no significant effect between two genotypes for 305 day-milk yield and open days.