The purpose of this study was to determine the effects of calf sex, birth type and birth month on birth weight using Regression Tree (RT) analysis. For this purpose, the data from 894 Holstein calves raised in Polatlı State Farm were analyzed. The birth weight of calves averaged 38.478 ± 2.487 kg. of total calves born, 95.5% were single born. Twin born calves weights were lower (35.125 ± 1.652 kg) than single born (38.635±2.408 kg). Male calves were significantly (P<0.05) heavier than females by 1.28 kg. The mean birth weight of twin calves was 3.58 kg lower than that of single calves. Effects of calving month, sex of calf, birth type on birth weight were all significant (P<0.05).