Growth performance as well as marbling is the main breeding objectives in Japanese Black cattle, the major beef breed in Japan. Researchers have recently reported that existence of Single Nucleotide Polymorphisms (SNPs), g.63629097G>C, g.120947716T>C and g.38437771C>T in the promoter regions of the septin 7 (CDC10), the insulin receptor substrate 1 (IRS1) and the mitofusin 2 (MFN2) genes, respectively in Japanese Black beef cattle population. The CDC10 is known to be involved in cellular proliferation and the IRS1 is reported to be associated with insulin resistance and birth weight. The 2 genes have been earlier shown to be located within genomic regions of quantitative trait loci for growth-related traits. Thus, the CDC10 and IRS1 genes were considered as positional functional candidates for the gene responsible for growth performance. In addition, the MFN2 is known to play a role in energy balance through mitochondrial fusion, so the MFN2 gene was considered as functional candidate. In this study, researchers analyzed the possible effects of the 3 SNPs on the growth-related carcass traits: Carcass Weight (CWT), Rib Thickness (RT), Rib Eye Area (REA) and Subcutaneous Fat Thickness (SFT) in Japanese Black beef cattle. The g.63629097G>C and g. 120947716T>C SNPs in the CDC10 and IRS1, respectively, exhibited significantly different allelic distribution between Japanese Black sires with extremely high predicted breeding value and the sires with extremely low one for CWT and RT but not for the others. The g.38437771C>T SNP in the MFN2 had significantly different allelic distribution for RT. These findings suggest possible effects of the g.63629097G>C, g.l 20947716T>C and g.38437771C>T SNP on the growth-related trait in Japanese Black beef cattle. The SNPs in the CDC10, IRS1 and MFN2 genes may be useful for effective marker-assisted selection to increase the beef productivity in Japanese Black beef cattle. © Medwell Journals, 2012.