The aim of this study was to investigate environmental factors affecting reproductive traits of Holstein cows and heifers raised at the Tahirova state farm in province Balikesir in Turkey. Reproductive traits were investigated by using 1074 records between 2000 and 2008. The least square means of age of first breeding, age of first calving, service period, calving interval and gestation length were 523.90 +/- 6.71, 815.38 +/- 7.18, 387.69 +/- 1.60, 122.30 +/- 1.67 and 277.45 +/- 0.27 days, respectively. Effects of calving year, calving age, calving season on age of first breeding and age of first calving were statistically significant (p<0.01). The effects of calving age, calving year and calving season on calving interval were significant (p<0.01-0.05). Although, the effect of calving year on service period was non-significant (p>0.05), the effects of calving age and calving season on service period were significant (p<0.01-0.05). Effects of sex of calf, calving age, calving year and calving season on gestation length were statistically significant (p<0.01-0.05). According to these results, it can be concluded that reproductive performance of Holstein cattle reared at this farm in Balikesir province were raised more successful than state farms in other regions of Turkey. To obtain better reproductive performance, service period should be decreased, heifers should be bred at 15 months of age, oestrus detection and artificial insemination should be done at the right time and convenient manner, GnRH injections was done for cows with high milk yield.