Abstract: One hundred and eight, 3 weeks old female quails were distributed among 3 treatments to study the effect of estradiol administration, on their productive and reproductive performance. Birds of the first group were intramuscularly injected at 3 weeks of age daily with 100 μg E₂/bird/day for 7 consecutive days. Birds of the second group were treated in a like manner starting from 5 weeks of age and the third group served as control. Birds injected with E₂ either at 3 or 5 weeks of age had a significantly higher body weight at sexual maturity and females injected at 3 weeks of age matured significantly earlier compared to control. Egg number egg weight and egg mass had significantly increased due to E₂ injection at both ages with females injected at 3 weeks of age having the highest values. Estrogen-progesterone ratio fluctuated with reverse relation to egg production. Tibia relative weight, length and calcium content were significantly increased by estrogen injection with birds injected at 5 weeks of age having the highest values. It can be concluded that treating immature Japanese quails with E₂ can enhance their reproductive and productive functions and that applying the treatment earlier (3 weeks of age) has better results when compared to applying it at 5 weeks of age regarding egg production, feed conversion and calcium metabolism.