This study was conducted to estimate the breeding value of sire for backfat thickness in swine by BLUP and least squares method, to estimate the correlations among the breeding values estimated by the two methods and to compare the efficiency of the two methods of estimating the breeding value. The data used in this study were obtained from 5,386 heads of Durocs, Landraces and Yorkshires tested on a weight-constant basis at S. Swine Breeding Farm in Icheon, Kyunggi-Do from August, 1982 to August, 1987. The results obtained in this study are summarized as follows. 1. The correlation between the breeding values of sire estimated by the BLUP and least squares method in male offspring was 0.778 and 0.799, respectively, in Durocs and Yorkshires, and the correlation in female offspring was 0.974 and 0.817, respectively, in the two breeds. These correlations were highly significant. 2. The correlations between the breeding value of sire estimated by the male offspring and the breeding value of the same sire estimated by the female offspring were higher in the BLUP than in the least squares estimates. 3. The BLUP appears to be more efficient than the least squares method in estimating the breeding value in view of the magnitude of the standard errors. 4. Although the BLUP is more efficient than the least squares method in estimating the breeding value, the least squares method may be used for the estimation of breeding value, if G^-1-value is not known correctly or if it is difficult to use the BLUP, in view of the positive and high correlations between the breeding values estimated by the two methods.