A6063 aluminum alloy was anodized in binary acid solutions, viz. tartaric acid, malic acid or malonic acid mixed with oxalic acid, for 20min by applying a constant c.d. of 5.65A/dm2 at 40 to 60°C. In the electrolytic bath containing only one component, uniform oxide film was not formed. Bath voltage during anodizing in the tartaric or malic acid bath was high (above 220V with 1mol/l and above 150V with 3mol/l), whereas in malonic acid bath it was relatively low (80-85V with 1mol/l). When 0.15-0.2mol/l oxalic acid was added to the 1mol/l baths of these acids, uniform, integral-colored, crack-free and hard oxide films of Hv 300-470 were formed at 40 to 50°C. The final voltage was lowered by the addition of oxalic acid in the baths of tartaric acid and malic acid (105-135V and 120-140V respectively), whereas in the bath of malonic acid the final voltage was scarcely changed with the addition of oxalic acid or slightly higher (78-95V). With increasing oxalic acid concentrations and elevating temperatures, the number of micropores of the film increased, leading to the decrease in hardness values.