This study was conducted to investigate the effect of concentrate feed level on the weight change, intestinal microbiota, and blood profiles of Jeju cross-bred horses. Jeju cross-bred horses, which are from twenty-four months to thirty-six old, were allocated three groups and were investigated by feeding the concentrate feed at 1.5% (n=5), 2% (n=4), and 2.5% (n=5) of their body weight in spring and winter. In spring, the final body weights were 288.60, 324.50, 337.00 in 1.5%, 2%, and 2.5% and its levels were significantly high in the treatment group (p<0.05), which were fed concentrate feed at 2.5% of body weight. In spring, endotoxin, which is known to be released in gram-negative bacteria cell wall in case of eating much concentrate feed, were 2.13, 1.50, and 0.57 in 1.5%, 2%, and 2.5% treatment groups respectively and its levels were significantly low in the treatment group which were fed concentrate feed at 2% and 2.5% of body weight (p<0.05) in the third week. But since then, there were no significant differences. The faecal pH were 6.2, 5.8, 5.7 in 1.5%, 2%, and 2.5% and its levels were significantly low in the treatment group in spring, which were fed concentrate feed at 2% and 2.5% of body weight. In the eighth week of winter, rectal temperature were 37.8, 37.9, and 38.4 in 1.5%, 2%, and 2.5% treatment groups respectively and its levels were significantly high in the treatment group which were fed concentrate feed at 2.5% of body weight (p<0.05). The number of faecal microbiota, such as Fibrobacter involved in the decomposition of cellulose and carbohydrates, were 2.49%, 1.42%, 1.09% in 1.5%, 2%, and 2.5%. It shows significant decrease as the amount of concentrate feed increased. These results suggest that feeding concentrate at 2.5% of body weight might be utilized as a method of fatting in Jeju cross-bred horses.