Ewe lambs born to group pen-fed Karakul ewes in the summer (February), winter (June) or spring (October) respectively, were raised to study the influence of season of birth on the onset of sexual maturity. Lambs were exposed to fertile rams from 90 days of age (weaning). Ewe lambs born in summer, winter or spring attained sexual maturity at a mean (± SD) age of 355,3 ± 22,6; 275,6 ± 41,9 and 225,4 ± 12,1 days at a mean (± SD) body mass of 53,3 ± 3,6; 40,6 ± 6,3 and 35,6 ± 4,2 kg respectively. Season of birth in this study had a highly significant (P<0.01) influence on age and body mass at first conception in Karakul ewes.