This study was conducted to determine the effects of sex, year of birth, season of birth, and the effects of breed or breed cross on birth weight in beef cattle. The data used in this study were obtained from a total of 1020 calves born at Chedong Farm in Cheju Island from 1974 through 1977. The Augus, Charolais and Hereford and their crosses were used, and the data were analysed by least squares method. The results obtained are as follows. 1. The birth weight of male calves was heavier than that of female calves by about 1.0 ㎏. 2. The effect of year of birth was statistically significant at 1% level. The birth weight of calves was lightest in 1974 when the Farm was in the first year after being established, and was heaviest in 1976. 3. The calves that were born in the spring had the heaviest birth weight, and those born in the fall had the lightest birth weight. 4. The Charolais had the heaviest birth weight of the three purebreds, being heavier than the Hereford by 0.4㎏, and the Angus had the lightest birth weight. Of the three crossbreds compared, the Charolais-Hereford cross had the heaviest birth weight, being heavier than the Hereford by 1.6㎏.