A water-soluble hyperbranched polyester with a considerable number of hydroxyl terminal groups was synthesized by reacting maleic anhydride and glycerol in the absence of a solvent. The synthesized intermediate product was converted to the hyperbranched polyester by condensation polymerization, and the water by-product produced during the esterification reaction may be removed by Vacuum distillation. In the synthesis process, the crosslinking reaction occurs readily if maleic anhydride is in excess. The result shows that the product synthesized by this one-step method is insoluble in water at room temperature, whereas the product of a quasi one-step method, in which pentaerythritol was added as a core molecule, has good water solubility when pentaerythritol and the raw material have a molar ratio of 1 : 100 or 1 : 150. The resulting hyperbranched polyester was purified by column chromatography and characterized by infrared spectrometry. The synthetic hyperbranched polyester was used at 0.5% as a crosslinking agent for acrylic ester to inform acrylic ester latex film; the water absorption of the film was decreased significantly, the viscosity was increased, and some mechanical properties were improved. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 3376-3381, 2009