Data on 820 Romanov lambs progeny of 30 sires it covered the period from 1995 to 2005 were used in this study. Lambs traits studied were birth weight (BW) body weight at one month (BW1), body weight at two months (BW2), weaning weight at three month (WW) and average daily gain from birth to weaning (ADG). Data were analysis by using mixed model. Means of BW, Bw1, BW2, WW and ADG were 2.90 kg, 7.10 kg, 10.50 kg, 13.02 kg and 115.50 g respectively. Sire of lambs, ewes within sires had a highly significant effect on all traits. Season and year of lambing, type of birth and sex had a significant effect on all studied traits, expect the effect 0f year lambing on BW and type of birth on BW1 and WW. Also, inbreeding coefficients had a highly significant effect on all body weight traits studied and decreased as inbreeding coefficient increased. Two animal models were used. Model 1 includes the fixed effects season and year of lambing, type of birth and sex and random effects of direct genetic effect, permanent environmental effect and residual effect. Model 2, is similar to model 1 and added maternal genetic effect and covariance between direct and maternal genetic effect.Determination of direct heritability for body weights traits ranged from 0.17 to 0.39 for model 1 and ranged from 0.13 to 0.29 for model 2. The removal of additive maternal effects and covariance between direct and maternal genetic effects (model 1) increased estimates of direct heritability. Therefore, including maternal effects the model resulted in more accurate estimation of (co) variance and genetic parameters of growth traits. Determination of phenotypic and genetic correlations among growth traits studied were moral and highly significant. While, annual phenotypic and genetic trends for body weights traits were negative.