In the present study data were collected from Seds experimental station of Animal Production, Ministry of Agriculture, during the years from 1995 to 2006 on local Saidi sheep. A total number of 1644 Saidi lambs records were available for this study. The data were analyzed by the method of Least-Square analysis. The study aimed to determine the effects of some environmental factors ( lambing season, lambing year, sex of lamb and type of birth ) and inbreeding on the weights of lambs at birth, monthly weight until 18 month and average daily gain in body weight at different periods of age, Bw-3, ˃3-6, ˃6-9, ˃9-12, ˃12-15 and ˃15-18 months. All weights at different age significantly affected (P<0.001) by the environmental factors except weights at the periods of 12, 16, 17 and 18th  for lambing season and at 15, 16 and 18 months for type of birth. The inbreeding did not had significant effect on body weights at different periods of age except the weight at one and two months of age were significant (P< 0.001). The average daily gain in body weight of Saidi lambs at all different periods of age were significantly affected (P<0.001) by lambing season, lambing year and sex of lamb except at the period of ˃12-15 months for lambing season were not significant. Results indicated that only the average daily gain in body weight at the periods of ˃Bw-3 and ˃3-6 months were influenced (P<0.001) by type of birth. The average daily gain at the period from birth to 3 months affected significantly by inbreeding (P<0.037). Therefore the non-genetic factors must be considered in evaluating growth performance in the case of increase the economic gain to avoid the breeding effect.