A study was conducted to examine the effect of genetic and non-genetic factors on pre-weaning growth in Marwari flock of 1649 sheep maintained at Arid Region Campus, Central Sheep and Wool Research Institute, Bikaner (Rajasthan). The least-squares means for birth weight, weaning weight and average daily gain from birth to weaning were 3.14±0.02 kg, 15.13±0.14 kg and 133.59±1.43 g/day, respectively. The least-squares analysis of variance revealed highly significant (P≤ 0.01) effect of sire, sex and period of birth on all the pre-weaning traits. Effect of parity was found significant (P≤ 0.01) only on birth weight. Dam's weight at lambing was a significant (P≤0.01) source of variation for all the traits.