Biodegradable particles for medical use and a vascular embolization material have improved flexibility, cause less aggregation among particles, and have improved particle shape-recovering ability after passing through a catheter or the like. The biodegradable particles for medical use are composed of an A1-B-A2 type triblock copolymer, wherein A1 and A2 are each a block of biodegradable copolymer constituted of monomers including glycolic acid, lactic acid and 6-hydroxycaproic acid, and B is a block of water-soluble polymer.