The purpose of the invention is to provide biodegradable particles for medical treatment and a vascular embolization material the inadequate softness of which has been improved the particles do not aggregate with each other easily and the particle shape restoring force after passing through a catheter etc. has been improved. The invention provides biodegradable particles for medical treatment obtained from a tri block copolymer of an A1 B A2 form wherein A1 and A2 are blocks of biodegradable copolymers configured from monomers comprising glycolic acid lactic acid and 6 hydroxycaproic acid and B is a block of a water soluble polymer.
