Abstract: The present research was carried out to determine milk yield traits and effects of environmental factors on these traits in Holstein cows raised at Polatli State Farm located in Ankara province. A total of 3011 production records between 1993 and 2006 were constituted the research material. Environmental factors were analyzed by Least Squares Method. Effects of parity (lactation number) on 305 days milk yield, lactation duration and dry period were significant (p<0.001-p<0.05). Effect of calving year on 305 days milk yield was significant at the p<0.001 level, nevertheless, not significant on both lactation length and dry period. Effect of calving year was significant statisticaly for all milk yield traits (p<0.001). Effect of calving age on 305 days milk yield and dry period were significant (p<0.001), nevertheless, not significant for lactation length. The least square means of 305 dayss milk yield, lactation duration and dry period were 5606.92±75.49 kg, 303.40±3.04 days and 98.15±2.25 days, respectively. Under Turkish conditions and steppe climate of middle Anatolia, it can be concluded that Holstein cattle are raised successfully for milk yield on Polatli state farm.