This study assessed the effects of the green seaweed Cladophora spp. as a protein source to substitute fishmeal protein in practical diets for postlarval tiger shrimp (Penaeus monodon). A control diet without containing seaweed meal was compared with fiveexperimental diets in which fishmeal protein was replaced by increasing the levels of green seaweed protein (10, 20, 30, 40 and 50%) in the diets. All diets were formulated to be equivalent in crude protein (40%) and lipid (7%). Each dietary treatment was replicated in triplicate. After 45 days of the feeding trial, urvival of the shrimp was not significantly influenced by the feeding treatments (p > 0.05). Growth rates of the shrimp fed with 10, 20, or 30%replacement levels of green seaweed protein in the diets were superior or similar to those fed with the control diet whereas shrimp fed with the diet containing 40 and 50% substitution levels showed significant reduction in growth (p < 0.05). The feed conversion ratio and protein efficiency ratio exhibited the similar trend as observed for growth performance. Moreover, shrimp fed with the control diet presented the lowest stress tolerance to formalin shock while the best performance was detected in the animals that received the 10 and 20% replacement diet. These results suggested that green seaweed Cladophora could replace up to 30% of fishmeal protein in the tiger shrimp postlarvae diet, and the optimal performance, including growth rate, feed efficiency, and stress resistance, appeared in shrimp fed with the diet of 10 to 20% substitution.