Abstract: The present research, was carried out to determine reproductive traits and effects of environmental factors on these traits in Holstein cows raised at polatli state farm located in Ankara province. A total of 2177 reproduction records between 1997 and 2006 were constituted the research material. Environmental factors were analyzed by least squares method. The least square means of gestation duration, first servicing period service period, NIPC and calving were 274.971±0.524, 111.55±3.73, 149.60±4.36, 1.72±0.05 and 427.88±4.36 days, respectively. On gestation duration, effects of breeding year, breeding age, birth type and sex of calf were significant (p<0.001). However, effect of breeding season on gestation duration was non-significant (p>0.05). Effects of breeding age on all reproductive traits (service period, first servicing period, Number of Insemination for Per Conception (NIPC) and calving interval) were significant (p<0.001). Effect of breeding season on service period and on calving interval was significant (p<0.05). However, effect of breeding season on first servicing period and on NIPC was non-significant (p>0.05). As effect of breeding year on all reproductive traits was significant first servicing period, management was the most important factor in this study.