Polyacrylic acid was synthesized and used as a retarder additive to prolong the setting time of gypsum plasters. The gypsum paste with the polyacrylic acid at the concentration of 0, 0.1%, 0.2%, 0.3%, 0.4% and 0.5% was studied. The water/gypsum mass ratio was 0.56. The influence of polyacrylic acid concentration on the initial and finial setting time, hydration temperature, morphology of hardened gypsum and mechanical property were extensively investigated. The results show that polyacrylic acid is favorable to increase the setting time which was associated with the reaction of carboxylic group and calcium from the hemihydrate dissolution. The morphology of hardened gysum varied when polyacrylic acid is used. The increase concentration of polyacrylic acid results in a decrease in hydration heat release, flexural and compressive strength.