In this research, growth traits (birth and weaning weight, and pre-weaning average daily gain) records collected from 11,837 Baluchi lambs (represented 300 rams and 3,694 dams) during 31 years (1978-2008) in two flocks of Abbas Abad breeding station, Mashhad were used . Probability of "more than the average" was modeled for some environmental factors using logistic regression for the traits. The overall average and standard error of birth and weaning weight, pre-weaning average daily gain were 4.32 (±0.007), 22.33 (±0.046) kg and 193.22 (±0.436) gr, respectively. The results indicated that year, sex and birth type of lamb had statistically significant effect on the probability of "more than the average" for all traits. Based on estimated regression coefficient, year of birth had negative effect on the probability associated with birth weight (-0.014) while it had positive effects on the probability of weaning weight (0.19) and pre-weaning average daily gain (0.017). Inbreeding was found to have negative effects on the probability associated with birth (-2.399) and weaning (-1.495) weights. Dam age at lambing had positive effect on the probability associated with birth weight (0.02). The probability associated with weaning weight (0.087) was found to be positively affected by weaning age.