Oxygen is known to be one of the major causes of oxidative degradations of nutrients. Ascorbic acid, a component of interest due to its health benefits, is reported to be highly oxygen sensitive. To understand better the influence of oxygen on ascorbic acid retention at canning temperature, thermal treatment was performed in model solution at pH=3.5 with varying partial pressure of oxygen from 0 MPa (strict anaerobic conditions) to 0.1 MPa in the headspace gas, from 95 °C to 125 °C, starting from an initial concentration of 900 mg/L. Treatment of 320 min was not sufficient to completely degrade all ascorbic acid initially present in the medium under anaerobic conditions and with a partial pressure of oxygen in headspace at 0.03 MPa, but treatment of 120 min was sufficient to degrade all initial ascorbic acid when the partial pressure of oxygen in headspace was set at 0.1 MPa. Apparent reaction orders were calculated; they were of 1 under anaerobic conditions, and 0.5 or 0.75 depending on partial pressure of oxygen. Activation energy was calculated using the Arrhenius law under anaerobic conditions only (Ea =67 kJ/mol). When oxygen is present, whichever its partial pressure in headspace, no acceleration of reaction was observed with increased temperature.