We used a half-sib family of purebred Japanese Black (Wagyu) cattle to locateeconomically important quantitative trait loci. The family was composed of 348fattened steers, 236 of which were genotyped for 342 microsatellite markersspanning 2,664 cM of 29 bovine autosomes. The genome scan revealed evidence of15 significant QTL (<5% chromosome-wise level) affecting growth and carcasstraits. Of the 15 QTL, six QTL were significant at the 5% experiment-wise leveland were located in bovine chromosomes (BTA) 4, 5, and 14. We analyzed thesethree chromosomes in more detail in the 348 steers, with an average markerinterval of 1.2 cM. The second scan revealed that the same haplotype of the BTA4 region (52 to 67 cM) positively affected LM area and marbling. We confirmedthe QTL for carcass yield estimate on BTA 5 in the region of 45 to 54 cM. Fivegrowth-related QTL located on BTA 14, including slaughter and carcass weights,were positively affected by the same region of the haplotype of BTA 14 (29-51cM). These data should provide a useful reference for further marker-assistedselection in the family and positional cloning research. The research indicatesthat progeny design with moderate genotyping efforts is a powerful method fordetecting QTL in a purebred half-sib family.