In dairy cattle, the increase in milk yield has been accompanied by a more negative energy balance during early lactation and a decrease in fertility. The 167 amino acid protein product of the ob gene was named leptin. The leptin hormone, as a 16-kDa protein is synthesized mainly by adipose tissue and is involved in regulation of food intake, energy balance, fertility and immune function. The expression and secretion of leptin are correlated with body fat mass and are acutely affected by changes in food intake. The objectives of this study was to investigate the fluctuations of leptin concentrations during late pregnancy and early lactation, effect of parity and BCS on plasma leptin concentration, and to investigate it’s fluctuation effects on milk yield, percentage of milk components and reproductive status. Blood samples of 54 Holstein cows were taken at a fixed time of the day after milking but before fooding from 2 weeks before calving until 6 weeks after calving. BCS and plasma leptin concentration were measured at 2-wk intervals. Leptin concentrations was affected by parity. Primiparous cows and cows in first parity had higher leptin concentrations compared with multiparous cows (p 0.05). Leptin concentration was not different in late pregnancy and early lactation. BCS was negatively correlated with plasma leptin concentration (p 0.05). Plasma leptin concentration did not influence milk production and percentage of milk components (fat, protein, and lactose), as well as reproductive traits (days in milk at first breeding, service per conception and open days).