Tissue homogenates of Ehrlich ascites tumor tissues and several normal tissue of mice were incubated separately in medium maintaining C¹⁴_acetate concentrations of 5, 10, 20, 30, 40, 50 and 60 mg%, in order to determine maximum oxidative rates of acetate. In every incubation experiments, respiratory CO₂ samples rapped by alkaline which was placed in the center well of the incubation blask were analyzed for total CO₂ Production rates and their radoactivies. The fractions of CO₂ from medium acetate to total CO₂ production rate were obtained with relative specific activities (RSA) which were calculated by ratio between specific activities (SA) of CO₂ and medium C¹⁴_acetate and CO₂ production rates from medium acetate were calculated from RSA and total CO₂ production rates. Maximum plateau values of oxidative rates described above were determined at incubation experiments of various concentrations of medium acetate and compared the oxidative rates of acetate of tumor with those of normal tissues such as kidney, brain and liver. Maximum plateau values of total CO₂ Production rates were obtained at acetate concentration of 20 mg% and represent 25.0±0.54 μM/hr/gm in the brain, 16.3±2.5 in the kidney, 9.1±1.78 in the liver and 11.5±3.2 μM/hr/gm in the ascites tuners. Substancial CO₂ yield was observed in the tumor tissues as in the normal tissues. On the other hand, plateau values of RSA were 25.7±1.04% in thee brain, 9.1±0.72% in the kidney, 2.5±0.73% in the liver and 0.51±0.12% in the tumor tissues. CO₂ yields from the medium acetate, were 4.19 in the kidney, 2.28 in the brain, 0.228 in the liter and 0.059 μM/hr/gm in the tumor tissue. These show wide range even in the normal tissue but remarkable decrease in the tumor tissue. This fact means that further oxidation of acetate was inhibited remarkably in the tumor tissue.