To investigate heterosis effect and reciprocal difference, the Whithe Leghorn(LL, sire breed being first), Australorp (AA) the reciprocal chicks(AL and LA) between these two breeds were compared with respect to early growth, chick mortality, feed consumption and feed conversion, from hatching to 8 weeks of age, using 338 male 366 and female chicks, and with respect to fertility and hatchability using 1437 hatching eggs. The chicks and eggs used were obtained from the purebreeding and crossbreeding of White Leghorns and Australorps. The differences in body weight between two purebreds (AA-LL) appeared significant after about 2 weeks, of age, and were 65.37±16.20 g, and 75.57±10.31 g, in males, respectively, at weeks of age. The Comparisons of the body weights between the reciprocal crossbreds, which showed the highly significant (P$lt;0.01) difference in females after hatching or 2 weeks of age, but not significant difference in males after 6 weeks of age, presumably suggested that sex-linkage was more important in determining the body weight at $quot;miniature$quot; broiler age (6-8 weeks of age) than maternal effects. The crossbreds were consistently heavier than the purebreds after 4 weeks of age, but a significant heterosis effect was not obtained with respect to the early growth. The AL crossing showed consistently lower fertility than the others, but the differences among the mating types were not statistically significant. The congenital maternal effects of two breeds as well as well as the effect due to the age of dam played an important role in determining hatchability. No conclusion was drawn with respect to chick mortality and feed consumption, since the results were divrgent from hatch to hatch. The AA and LA chicks were significantly more efficient in feed conversion than the LL, chicks. The differences in feed conversion were mainly attributed to the body weights at weeks of age.