PURPOSE: To obtain the subject composition capable of readily controlling biodegradability and coping with the fields different in requirement to biodegradation rate by change, etc., of amount of an acid compound, which composition is obtained by blending cellulose acetate with an acid compound having an acid dissociation constant larger than that of acetic acid.

CONSTITUTION: The objective composition consists of (A) cellulose acetate and (B) 0.01-10wt.%, preferably 0.1-5wt.% acid compound having an acid dissociation constant larger than that of acetic acid. The composition is preferably blended with 20-50% plasticizer in order to enable thermoforming. As the plasticizer, polyethylene glycol is preferably used from the viewpoint of biodegradability.