In Japan and Korea, highly marbled Wagyu and Hanwoo cattle are greatly prized for traditional meat cooking methods. Their marbling has been increased to meet domestic consumer preferences. Many researches have shown that Wagyu and Hanwoo cattle have high potential of accumulating IMF and producing highly marbled beef. The beef quality grading system in both countries is primarily determined by marbling score with BMS and additionally adjusted by other carcass traits. Literature suggests that IMF content varies on the basis of feeding time, finishing diet, and breed type. Great attention has been paid to more accumulation of IMF to produce high quality grade beef. It is clear that IMF increases with increased feeding time. The rate of IMF increase in grain-fed cattle is faster than that in pasture-fed cattle. Literature also indicates that fatty acid composition varies between breeds. Highly marbled Wagyu and Hanwoo beef have higher proportions of MUFA due to higher concentrations of oleic acid. Many studies have shown that MUFAs have little effect on total cholesterol. They are heart-healthy dietary fat because they can lower LDL-cholesterol while increasing HDL-cholesterol. Clinical trials have also indicated that highly marbled beef does not increase LDL-cholesterol and that beef high in oleic acid can consistently increase HDL-cholesterol. Finally, literatures have concluded that high-oleic acid beef such as Wagyu and Hanwoo beef may reduce risk factors for cardiovascular diseases.