AbstractIn general, polymers that enhance the mechanical strength of gypsum plaster simultaneously decrease its water absorption capability. In this research, starting from polyvinyl acetate (PVAc) and polyvinyl alcohol (PVA), respectively, two groups of PVA-derived polymers were, partially hydrolyzed polyvinyl acetates (PHPVAs) and polyvinyl alcohol sulfates (PVAS). The modulation of mechanical strength and water absorption of gypsum plaster with PHPVA and PVAS was studied. Their structure–property relationship was investigated. Except for morphology, the influence of product structure on the mechanical properties of the hardened gypsum plaster was studied, including mechanical strengths, dynamic water absorption, hydration degree, and hydration temperature. The mechanical strength initially increased with increasing hydrolysis or sulfonation degree but eventually decreased. The water absorption capability was proportional to the hydrolysis degree but was not significantly related to sulfonation degree. PVAS are the optimum candidate for modeling material, whereas PHPVA is optimal for construction materials. By molecular modification of PVA, highly enhanced mechanical strength can be realized with modulatable water absorption of the hardened gypsum plaster.