The study was conducted to estimate the heritabilities, genetic, phenotypic and environmental correlations among preweaning body weight in swine. The data analysed were the record of 253 males pigs produced from 57 boars of Landrace, Hampshire, Large Yorkshire and Duroc purebred raised at the National Animal Breeding Institute from 1978 to 1983. The results are summarized as follows. 1. Duroc was rather heavy with 1.595㎏ in birth body weight and Landrace was superior with 6.508㎏ and 22.459㎏ in the body weight at 21days and 56days, respectively 2. The heritabilities of body weight at birth, 2ldays and 56days of age were 0.233, 0.485 and 0.758, respectively. 3. Genetic correlations between at birth weight and 21days and 56days weight were 0.349 and -0.098, respectively. Genetic correlation between body weight at 21days and 56days was 0.907. 4. Phenotypic correlations between body weight at birth and at 21days and 56days were 0.334, and 0.287, respectively. Phenotypic correlation between body weight at 21days and 56days were 0.576. 5. The results obtained in this study suggest that individual selection for body weight at 21days and 56days could be achieve considrable amount of genetic improvement.