Present investigation was carried out to study the influence of genetic and non-genetic factors affecting post-weaning performance traits in Thalli sheep. Data on post-weaning growth of Thalli sheep maintained at Livestock Experiment Station, Rakh Ghulaman, District Bhakkar-Punjab, Pakistan during 1977-2003 were subjected to genetic analysis. The average values for weight at 180 and 270 days of age, yearling weight and post-weaning average daily gain were 22.37 ± 4.21, 25.96 ± 4.90 and 28.93 ± 5.20 kg and 28 ± 0.01 g/day, respectively. Weight at 180, 270 and 365 days of age and post-weaning average daily gain were significantly affected by year of birth, sex, type of birth and weaning weight (covariable) whereas season of birth was a significant source of variation for 180 and 270 days of age. The heritability estimates for 180 and 270 days, yearling weight and post-weaning average daily gain were 0.07 ± 0.02, 0.08 ± 0.02, 0.07 ± 0.02 and 0.07 ± 0.02, respectively.