Our previous study showed that acetic acid was a stable intermediate of the oxidation of various food wastes in supercritical water. These results indicated that acetic acid can be obtained as a product and can be increased by optimizing the reaction condition, but there was a limit to the yield of acetic acid, i.e. only 11-13 % at most on a carbon basis. To enhance the production of acetic acid from carbohydrate biomass, a new two-step process was proposed. This process consists of both a hydrothermal reaction without oxygen and an oxidation reaction. The first step is to accelerate the formation of selected intermediates which can produce a large amount of acetic acid by their own oxidation, and the second step is to convert these products formed in the first step to acetic acid by oxidation. The result showed that the acetic acid yield was greatly increased by this process.