an aqueous dispersion of a biodegradable polyester , which comprises a copolymer of 3 - hydroxybutylate and 3 - hydroxyhexanoate having a weight average molecular weight of 50 , 000 to 3 , 000 , 000 and a flexural modulus of 100 to 1500 mpa , wherein the copolymer has an average particle diameter of 0 . 1 to 50 μm in the aqueous dispersion . the aqueous dispersion of a biodegradable polyester is excellent in film forming characteristics and can provide a resin coating film which is soft , exhibits good elongation and is proof to bending , when it is applied to a coating material , an adhesive agent , fiber texturing , sheet or film processing , paper conversion or the like .