The power of dried seaweed Gracilaria sp. was supplemented to experimental feeds at different levels from 0% to 10% for rearing of grass shrimp, Penaeus monodon. After 120 days, the survival rates were between 57.5% and 67.5%, not significantly different among groups. The weight gain and feed coefficient were higher in the 3% group than those of other groups. Supplementation of appropriate amount of Gracilaria sp. in feed will increase the concentration of highly unsaturated fatty acids in shrimp body and enhanced the growth and survival rate of grass shrimp.