Japanese native cattle, including improved breeds, are generally called "Wagyu". They have been kept for one thousand or more years in Japan and used as cultivating and transporting labour. Some of them had been crossbred by European breeds in the late 19 th century or in the first decade of the 20th century. They were then divided into four breeds, namely Japanese Black, Japanese Brown, Japanese Poll and Japanese Shorthorn. Some of the breeds have included many line bred strains. Since about 1960 their use has been limited to the beef only, for their role of labour have been replaced by cultivating machines, breding of the beef producing character in "Wagyuu" cattle had started then. Official progeny tests and performance tests of sires have rapidly improved daily gain and meat quality. But the results of official progeny tests have not accurately represent-ed the genetic ability of sires, which are show in the least-squares analysis of variance for marketing carcass of the sons. It is necessary to collect much date from marketing carcasses, in order to genetically analyse the data and to select sires using the results of this analysis. Heritability estimates and genetic correlation calculated by many workers in Japan were summarized in this paper. In Japan, the unit price of the carcass varies greatly according to the marbling score ; therefore, most cows are tend to be mated to sires that have proved their excellent marbling ability. Most of these sires are the offsprings of only limmited sires belonging to a few strains. It is feared that a cow in a few generations might be related to every potential, desirable mate. Inbreeding depression might delay improvement. Then the author recommends to developing several strains in "Wagyu" cattles, and to mate them rotationally.