Lower salinity acclimation of hatchery-reared Penaeus keruihurus postlarvae was investigated in short and long term experiments at PL20, PL30, PL40 and PL50. In short term experiment, the salinity tolerance was determined with/without acclimation. In tolerance test without acclimation, PLs were transferred suddenly from 36 ppt to 2, 5, 10, 20 and 30 ppt. In tolerance test with acclimation, PLs were acclimated over four days from the reared salinity (36 ppt) to 2, 5, 10 and 20 ppt. After acclimation, PLs were transferred from acclimated salinities to lower and higher salinities. In both tolerance testes, PLs were kept for 96 hr. It was found that acclimation has a significant effect in some cases at PL30 and PL40. In both tolerance tests, the highest salinity tolerance (80-90 % survival rate) was attained at PL50 in salinity range of 10-36 ppt. In long term growth experiment. PLs were reared at 5. 10, 20 and 36 ppt for 30 days using minced clam meat. The highest specific growth rate (SGR), survival and production were recorded at the salinity range.of 10-20 ppt.