Lipase-catalyzed reaction of 3-hydroxybutyric acid with d-glucono-δ-lactone at 5:1 molar ratio and 80 °C yielded a mixture of moderate molecular weight linear and cyclic oligomers. The most efficient biocatalyst, Candida antarctica B lipase (Novozyme 435), allowed the synthesis of new oligomeric compounds with ring-opened gluconolactone units included in the oligomeric chain, without previous derivatization of the sugar, or activation of the acid monomer. The reaction medium nature had an important influence on the product composition. Although the main copolymer amount was synthesized in tert-butanol/dimethylsulfoxide medium, the highest polymerization degrees, up to 9 for the copolymer, and 10 for the 3-hydroxybutyric acid homopolymer co-product, were achieved in solventless conditions.Graphical abstractLipase-catalyzed polymerization reaction of 3-hydroxybutyric acid and d-glucono-β-lactone yielded. (a) Linear oligomers with inserted gluconolactone units; (b) cyclic oligomers with inserted gluconolactone units; (c) homopolymers of 3-hydroxybutyric acid.Highlights► Copolymerization of 3-hydroxybutyric acid and d-glucono-β-lactone was catalyzed by lipase in various reaction media. ► Linear and cyclic oligomers were synthesized at 80° in argon atmosphere. ► Such functionalized oligomers can emerge as new biomaterials.