A polylactic polyester resin having a chemical structure represented by Formula (1), an acid value of 300 to 2,500 eq/106 g, a number average molecular weight of 2,000 to 50,000, and a lactic acid content percentage of not less than 40 weight %, Z—(O—(CH2CH2O)p—(CO—Y—O)q—X)r  (1) wherein Z is an r-valent organic group, Y is —CH(CH3)—, or a mixture of —CH(CH3)— and C2-10 linear or branched alkylene group, and X is a residue of a polybasic acid having 2 or more carboxyl groups, or hydrogen; each of X, Y, and Z may be one kind or a mixture of a plurality of different kinds; and p, q, and r are 0 or a positive integer, p has an average value of not less than 0.5, q has an average value of not less than 5, and r has an average value of not less than 3 and not more than 15. An aqueous dispersion, an aqueous resin composition, an aqueous adhesive, an aqueous paint, aqueous ink, a laminate made of an aqueous adhesive or aqueous ink, a packaging material, a sustained-release biodegradable coating agent, and a sustained-release biodegradable coated body comprising the sustained-release biodegradable coating agent, which contain the polyester resin.