This study aimed to remove residual chlorine in chlorinated seawater for rearing Penaeus monodon larvae and algae by aeration method. The results show that chlorine can be removed gradually by aeration. The residual chlorine level is negatively correlated with the aeration time. The residual chlorine added at 1.8 mg/L available chlorine to seawater can not be detected after 24-hour aeration. Therefore, chlorinated seawater can be used for culturing algae, washing eggs and rearing larval shrimp. However, different aeration time is needed due to various tolerances of organisms to residual chlorine. The 24-hour aeration, with resulting residual chlorine level <0.05 mg/L, of chlorinated seawater is necessary for rearing P. monodon larvae. For culturing Nannochloropsis oculata and Skeletonema costatum, aeration for 2 hours (residual chlorine level <1.5 mg/L) and 12 hours (residual chlorine level <0.8 mg/L), respectively, is adequate. In addition, fertilized eggs of P. monodon disinfected with 1.8 mg/L available chlorine for less than 20 minutes does not have any negative effect on the hatching.