In order to clarify the changes of meat quality with fattening stages of Japanese Brown steers, the authors sampled 32 steers fed high plane of nutrition from 6.2 to 31.6 months of age, and analized the relationships between meat quality (marbling score, meat color and meat texture·firmness) and month of age, finishing weight or the growth pattern of main tissues in the carcass.<BR>The correlation coefficients between meat quality (MQ) and weight of the fat in the carcass or its proportion to carcass weight (FP) were higher than the other coefficients between MQ and final age (FA), finishing weight (FW) or other tissue weigts in the carcass etc. It was suggested that changes of meat quality were closedly related to the growth of adipose tissue in the carcass.<BR>The relationships between MQ and FA, FW, or FP were analized using regression models of intersecting straight lines by OOTSUKA. In any case, there were two intersecting points, and from the first point to the second scores of MQ rose rapidly. After the second point the rate of scores increase become very slow and variations of data were larger than before this point, especially in marbring score. The second intersecting points which were considered as the peak of MQ improvement were estimated 16.9-17.9 months of FA, 535-555kg of FW and 25.4-25.7% of FP respectively. These points were attained at earlier age than the current age of finish.<BR>Consequently, it was clear that MQ was improved rapidly with age and growth of tissues, especially adipose tisuue in the carcass, and the rate of MQ improvement become very slow after the peak (the second intersecting points) .