Japanese Black cattle are the predominant beef breed in Japan. This breed has excellent meat quality, especially degree of (intramuscular) marbling. Degree of marbling was measured at the 6th to 7th rib section and according to the Beef Marbling Standard with scores 1 to 12 (so-called BMS), with number 12 being the best. BMS is used with business deal of beef carcass and has strongly effect on selling price of carcass. On the other hands, more degree of marbling on top round (MTR) is better carcass unit price in same BMS, because of good price of part of thigh. MTR has been focused in recent years. However, MTR is unclear how to evaluate, therefore, collection of records and genetic evaluations are not enough. In this study, records of MTR were collected and then, genetic parameters for BMS and MTR of Japanese Black were estimated. The original data were 11,052 carcass records collected from April in 2008 to June in 2009 at the Agura Farm. Only information from abattoirs having more than 20 records and feedlot farms having more than 10 records were used. This resulted in a total of 10,990 records. In this study, pedigree information was traced back to two generations. An animal model that included all relationships among all animals was used as a statistical model. The fixed effects included sex, farm, abattoir and the combination of slaughter year and month. Slaughter age was fitted as linear covariables. Genetic parameters were estimated using REMLF90 and THRGIBBS1F90 programs. The estimates of heritability were moderately high (0.37 to 0.44) for MTR treated as threshold traits. The estimates of phenotypic and genetic correlations between BMS and MTR were very high (0.87 and 0.98, respectively). These indicate that MTR can be improved genetically and improvement of MTR can treat BMS as indicator.