Objectives:This study investigated the effect of water storage on residual MMA content of acrylic resin specimens polymerized by heat-(long and short-term terminal boiled and conventional method using MeliodentTM), autopolymerization (at room temperature and in water bath at 60 ºC using Meliodent Rapid RepairTM) and microwave energy (at 500 Watts using Acron MCTM). Methods: Residual MMA content of 120 specimens was determined using high-performance liquid chromatography; at deflasking, and after stored in water at 37°C for 1 day, 1 week, and 1 month. Results: Residual MMA content started to reduce first in heat-polymerizing and autopolymerizing specimens processed in water bath at 60 ºC at the end of water storage for 1 day (p<0.05); then in autopolymerized specimens processed at room temperature at the end of 1 week (p<0.01); and at last in microwave-polymerizing specimens at the end of 1 month (p<0.01). Conclusions:Different polymerization methods and cycles had different effects on the reduction of residual MMA content of acrylic resins when stored in water.