PURPOSE: To obtain a modified biodegradable polymer composition excellent in flexibility, elasticity, impact strength, environmental protection, etc., and useful for a packaging material, a medical material, a cosmetic container, etc., by compounding a polylactic acid with a stabilizer, a plasticizer and a modified silicone.

CONSTITUTION: This composition is obtained by compounding (A) a polylactic acid, (B) a stabilizer such as sodium lactate, calcium lactate, zinc lactate, lead lactate, barium lactate, aluminum lactate, ferrous lactate, silver lactate, magnesium lactate, manganese lactate or copper lactate, (C) a plasticizer such as di-2-ethylhexyl azelate or di-2-ethylhexyl adipate and (D) a modified silicone such as a methylstyryl-modified silicone or an alkyl-modified silicone.