Partial oxidation of acetaldehyde by oxygen in the liquid phase was studied in the temperature range from −10 °C to 34 °C, oxygen flow rate from 90 to 100 mL/min, concentration of acetaldehyde from 3.0 to 34.0 volume percent, and at different partial pressures of oxygen. Cobalt acetate was used as catalyst. It was found that the reaction rate was governed by two types of rate equations depending on the operating conditions as well as the loading of catalyst.In the region of higher oxygen mass transfer, the rate[Formula: see text]where K1 = 6.9 × 10−3 L mol−1 s−1 at the temperature −10 °C.In other conditions,[Formula: see text]where k2 = 5.7 × 10−4 mol L−1 atm−1 s−1, and is a pseudo rate constant which depends on the dispersion of oxygen in the reactor. The experimental results appeared to support a theoretical analysis. The key reaction steps of the reaction mechanisms were also identified.