PURPOSE: To properly remove stain, unevenness and contamination generated on an anodized film, by executing hole-sealing treatment to said film, and after that, washing it by use of a specific aqueous carboxylic acid solution.

CONSTITUTION: A substance to be treated, which has coated aluminum with an anodized film is subjected to boiling water hole-sealing treatment by ion exchange water and a hole-sealing agent of nickel acetate. Subsequently, it is washed by one aqueous carboxylic acid solution selected among oxalic acid, malonic acid or maleic acid. Concentration of carboxylic acid is usually 0.01W 1.0mol/l, and if possible, the substance to be treated is soaked suitably at temperature from room temperature to about 80°C and for time from several seconds to about 20min. Also, wiping can be performed by use of cloth steeped in the aqueous carboxylic acid solution.