The aim of this research were to study the effect of weaning age and weight on post-growing rate (PWG) and to estimate the optimal weaning age (WA) and weight (WW) of Morada Nova-white variety breed lambs raised under extensive system conditions. A total of 31 male and female lambs were evaluated, being 19 lambs born in April/May 2001 and 12 lambs born in February/March 2002. Lambs were distributed in the following treatments at weaning: 1) weaning age = T1: weaned at 60 days; T2: weaned at 75 days; T3: weaned at 90 days, and 2) weaning weight = T1: weaned with 9 to 10.4kg weigth; T2: weaned with 10.5 to 12.4kg weight and T3: weaned with above 12.5kg weight. The PWG was recorded through successive weightings done every fourteen days from weaning to 180 days of age. Data were analysed through a statistical model that included age and weight at weaning, sex and year of birth as fixed effects. Lambs weaned with 60, 75 and 90 days of age showed non-significant differences (P>0.05) on PWG. However, WW had a significant influence (P<0.05) on lamb weight. The group weaned with 9-10.4kg had smaller live weight than those weaned with 10.5-12.4kg or above 12.5kg. No differences were found between these last two groups. Also, sex had significant effect (P<0.05) on lamb growing with males being heavier than females (20.7kg and 17.6kg, respectively). Year of birth did not affect PWG. It was concluded that weight at weaning is more important than age at weaning on post-weaning growing of lambs. The most efficient live weaning weight on white Morada Nova lambs raised in extensive system production is over 10.5kg.