Effects of breed, sex, and birth weight on growth and carcass composition traits were investigated using purebred Duroc, Landrace, and Yorkshire, respectively. Twenty-three sets of thee littermates, consisting of a boar, gilt, and barrow for each of 3 breeds was used. All pigs were classified into 3 groups based on their birth weights (BWT): small (mean = 1.15 kg), medium (mean = 1.50 kg), and big (mean = 1.75 kg). Gilts and barrows from each littermate were slaughtered at 103.40 kg (SD = 13.98 kg) of body weight. A mixed model that included fixed effects of breed, sex, birth group, interaction of breed and sex, and random effect of animal was used. Breed significantly affected growth traits. Landrace pigs had the highest (P < 0.05) overall average daily gain than in other 2 breeds. The overall average daily gain was 608.93 ± 7.87 g, 649.00 ± 7.82 g, and 603.38 ± 8.61 g for Duroc, Landrace, and Yorkshire, respectively. Heavier pigs at birth showed significant advantage (P < 0.05) on overall average daily gain (small = 595.99 ± 12.00 g, medium = 615.64 ± 6.17 g, large = 649.68 ± 7.65 g). Carcasses from Landrace pigs had thinner average backfat and tenth rib backfat thickness than those from Duroc breeds. Duroc pigs however had heavier (P < 0.05) ham weight than that of Landrace pigs indicated the carcass characteristics of Duroc breed. Most carcass composition traits did not show the sex effect except for fat percentage and weight of tenderloin (P < 0.05). Pigs with heavier birth weight had larger (P < 0.05) Boston butt. In conclusion, the results suggest that breed, sex, and birth weight are important sources of variation for growth and carcass composition traits of pigs.