Description: The impregnation of sheep at an early age is important for obtaining additional production of sheep (milk and lambs). The purpose of this study was the induction of synchronized oestrus and the comparison of the insemination and fertility of female lambs at 18 months of age and female lambs at 7-8 months of age in the current year of birth, using progesterone vaginal tampons in combination with serum gonadotropin (PMSG). In the experiment were used 30 female lambs of 18 months of age, with body weight of 48-50 kg and 30 female lambs of 7-8 months of age, with body weight of 38-40 kg of the Pleven Blackface sheep breed. After the 12-day stay of the vaginal tampons, and after their removal and treatment with PMSG, 98.3 PROCENT of the sheep have shown signs of oestrus between 48 and 60 hours. It is observed that the impregnancy of those that have shown signs of oestrus is 69.0 PROCENT (female lambs of 7-8 months of age), while with female lambs of 18 months of age the impregnancy is higher - 83.3 PROCENT . The biological fertility, expressed by the number of lambs live born compared to the number of births is 160 PROCENT with the female lambs of 7-8 months of age, while with the female of 18 months age, it is lower - 128 PROCENT . The average impregnancy and fertility in both groups of animals is respectively 74.6 PROCENT and 142.2 PROCENT . There were no significant differences in the duration of pregnancy in female lambs at 7-8 months and female lambs at 18 months, respectively -147 and 149 days. The number of lambs of the same mother (type of birth) had no effect on the duration of pregnancy