The lipase-catalyzed preparation of poly(1,6-hexanediyl maleate) by transesterification of 1,6-hexanediol and dimethyl maleate is described. A configurationally pure poly(1,6-hexanediyl maleate) exhibiting exclusively cis structure was obtained. During the reaction, a substantial amount of macrolactones was formed. They were isolated, and the cyclic oligomer with y = 2 was found to predominate. Cycles are semi-crystalline, while no melting point was detected for the linear poly(1,6-hexanediyl maleate). We assume that the linear unsaturated polyester is completely amorphous owing to its cis configuration.