A total of 864 hatching eggs of each strain of White Leghorn, Gimmiza, Mandara and El-Salam. was subjected just before incubation to gamma-irradiation at dose levels of 0, 0.25, 0.50, 1.00. 2.00.4.00. 6.00 and 8.00 Gray. Hatchability. R.B.C's W.B.C's, Hb, P.C.V., plasma total proteins, al-bumin, globulin and liver enzymes including ALT, AST and alkaline phos-phatase were determined at hatching. Exposing fertilized eggs to gamma-radiation up to 4 gray im-proved hatchability. More than 4 gray caused hatchability depression. Mandara was the most resistant strain to the harmful! effect of the high doses of gamma-rays. The hematological parameters such as R.B.C's count and P.C.V.% were decreased, while, W.B.C's count was increased. Strains were vari‌able in their response to the irradiation concerning these parameters. Plasma total proteins, albumin, globulin. G.P.T. and G.O.T. levels were significantly affected by irradiation of the fertilized eggs. Signifi‌cant differences between strains were also detected. Keywards: Gamma-radiation, chicken. hatchability and blood parameters.