The objectives of the present study were to analyze different environmental factors affecting pre-weaning growth performance of Mengali sheep. Performance records on 2377 lambs in four flocks maintained at Experimental Station, Centre for Advanced Studies in Vaccinology and Biotechnology, Quetta (ESC), Mastung, Nushki and Quetta area over a period of 5 years (Jan 2005 to Dec 2009) were analysed. Body weights at birth (BW), 30 days (1MW), 60 days (2MW), 90 days (3MW), 120 days Weaning weight, (WW), and pre-weaning average daily gain (PRADG) were evaluated. Location of flock, year of birth (YOB), season of birth (SOB), type of birth (TOB), sex and their interactions were the fixed effects in the model. The overall average values for BW, 1MW, 2MW, 3MW, WW, and PRADG were found as 3.54±0.37, 7.96±0.91, 11.77±1.83, 15.51±2.86, 19.16±3.23 kg, and 135.00±0.26 g, respectively. Location of flock, sex, and TOB had significant influences (P0.05) on weights at all ages. Flock kept at ESC (Quetta) location showed better performance for all traits as compared to other flocks. The difference might be attributed to regular supplementation of ration to this flock. Male lambs were heavier than female lambs, and single born lambs were also significantly heavier than twins (P<0.05) at birth. Results reflected that Mengali breed can be improved through selection and better management.