A total of 1528 Gimmizah chicks were used in the present study and divided into four main groups: A, B, C and D according to age to in­vestigate the response of birds to tamoxifen (TAM) injection at doses of 0.0.5,5.0 and 10.0 mg/kg.Bw. Group A started receiving TAM injections at the age of one week, meanwhile, the other three groups B,C and D started TAM injections at the age of 5,9 and 13 weeks consequently. In­jections were applied intraperitoneally once each three days for six suc­cessive weeks. Experimental results indicated that testes and oviduct relative weights were significantly increased due to TAM injections at doses of 0.5 mg, and 10 mg respectively, in group (A), but ovarian relative weights were not significantly affected with TAM injections. No significant differences in plasma total lipids could be detected due to doses or sex of birds at the age of one week, but. TAM injection significantly increased plasma total lipids in group (C) and TAM 5 mg in group (B). In all groups plasma cholesterol and total lipids levels in fe­males were higher than males. TAM injection at any dose had not significant effect on estradiol levels. Plasma testosterone was significantly by reduced due to TAM 0.5 mg in groups (A and B). but, all TAM doses significantly increased plasma testosterone levels in group (D). TAM doses applied had not significantly affected spermatogensis in males, while, viability in TAM doses were sig­nificantly lower than control in group (A). Moreover, vitality was in­creased significantly due to TAMS mg in group (D). Chicks weight at hatch was the only trait that significantly by varied in groups (A and C), but, no significant differences among treatment could be detected for fertility, hatchability, pipped, late dead and early dead percentages.