To provide a method for recovering a high quality cellulose plastic at low cost by removing colored foreign matter and insoluble content (including gel generating foreign matter) when doped in a short processing time.

Cellulose plastic mainly comprising a lower fatty acid ester of cellulose and containing impurities is processed in an aqueous solution containing both at least one peroxide and at least one transition metal compound or in an aqueous solution containing at least one halide oxide and bromo anion and/or iodo anion.