The data from 222 cattle raised by farmer of Cheju Island from 1964 to 1968 in a crossbreeding project involving Cheju Cattle, Brahman-Cheju Cattle crosses and Santa Gertrudis-Cheju Cattle crosses were analysed by least squre method. The result obtained are as follows: The birth weight of Brahman-Cheju Cattle crosses was heavier than that of Cheju Castle by 4.3㎏, and the Santa-Cheju cattle cross was heavier than the Cheju cattle by 4.14㎏. At three months of age, the Brahman-Cheju Cattle cross was heavier than the Cheju Cattle by 11.89㎏, and the Santa-Cheju Cattle cross was heavier than the Cheju Cattle by 9.97㎏. At six months of age, the Brahman-Cheju Cattle cross was heavier than the Cheju Cattle by 16.60㎏, and the Santa-Cheju Cattle cross was heavier than the Cheju Cattle by 16.5㎏. At 12 months of age, the Brahman-Cheju Cattle cross was heavier than the Cheju Cattle by 43.10㎏, and the Santa-Cheju Cattle cross was heavier than the Cheju Cattle by 45.89㎏. At 24 months of age, the Brahman-Cheju Cattle cross was heavier than the Cheju cattle by 53.38㎏, and the Santa-Cheju Cattle cross was heavier than the Cheju Cattle by 60.48㎏. The differences between the purebred Cheju Cattle and crossbreds were highly significant. But the differences between the Brahman-Cheju Cattle cross and Santa-Cheju Cattle cross ware unimportant. The males were heavier than the females by 0.77㎏ at birth, 2.45㎏ at 3 month, 3.73㎏ at 6 months, 11.26㎏ at 12 months and by 14.06㎏ at 24 months of age. The weight of calves from young dam tended to be smaller than those from the mature dam.