The study was conducted to estimate the heritabilities, genetic and phenotypic correlations on preweaning body weight and postweaning traits. The data analysis were the record of 253 male pigs produced from 54 boars of Landrace, Hampshire, Large Yorkshire and Duroc purebreds raised at National Animal Breeding Institute from 1978 to 1983. The results obtained in this study are summarized as follows. 1. The heritabilities of body weight at birth, 21days and 56days were $0.233{\pm}0.160$, $0.485{\pm}0.185$ and $0.758{\pm}0.214$, respectively, and the heritabilities estimated on postweaning traits were $0.270{\pm}0.164$ for average daily gain, $0.350{\pm}0.174$ for feed requirement, $0.272{\pm}0.165$ for backfat thickness, $0.887{\pm}0.221$ for days to 90Kg and $0.565{\pm}0.195$ for selection index. 2. Genetic correlations of body weight at birth with 21 days and 56 days were 0.349 and 0.19& and body weight at 21 days with 56 days was 0.907, and daily gain with feed requirement, backfat thickness, days to 90 Kg and selection index were -0.552, 0.107, -0.903 and 0.716, and feed requirement with backfat thickness, days to 90Kg and selection index were -0.058, 0.699 and -0.942, and backfat thickness with days to 90 Kg and selection index were -0.237 and -0.025, respectively. 3. Phenotypic correlations of body weight at birth with 21 days and 56 days were 0.342 and 0.287, and body weight at 21 days with 56 days was 0.893 and daily gain with feed requirement, backfat thickness, days to 90Kg and selection index were -0.062, 0.093, -0.651 and 0.540, and feed requirement with backfat thickness, days to 90Kg and selection index were 0.105, 0.601 and -0.613, and backfat thickness with days to 90Kg and selection index were -0.040, -0.416, respectively.