Effects of dietary supplementation of red macroalgae Gracilaria pygmea on the growth performance, hematology and serum biochemistry parameters of Asian Seabass Lates calcarifer with initial fish weight of 28±5.9 g were investigated in a 6-week experiment. The experimental diets were composed of the positive control diet (containing fishmeal), the negative control diet (containing fishmeal-soy protein) and three diets which supplemented with varying leves of red algae (3, 6 and 9%). Results indicated that daily growth rate, feed conversion ratio and final weight of fish not only were not negatively affected by different substitution levels of red algae, but also the final weight of fish fed the diet containing 6% red algae was higher than the other experimental diets. Condition factor of the negative control group and the specific growth rate of the treatment containing 6% red algae were significantly higher than those of the other experimental diets (P<0.05). Results of hemoglobin, hematocrit, White Blood Cell (WBC) count and WBC differential count were not significantly different among various treatments (P>0.05). Among the examined serum biochemistry parameters of Asian Seabass, only glucose was not significantly affected by various dietary treatments (P>0.05). The cholesterol levels of the negative control group and fish fed the diet containing 9% red algae were similar with each other and were significantly higher than the other treatments (P<0.05). The lowest level of albumin was observed in the treatment containing 6% red algae, whearese the lowest amounts of total protein, triglyceride and cholesterol were observed in the treatment containing 3% red algae. Overall, it seems that partial substitution of expensive fishmeal by red algae Gracilaria pygmaea in the diet of carnivorous  Asian Seabass exerted no negative effects on the growth and immunity parameters. Moreover, some growth parameters, hematological and serum biochemical parameters of blood were improved by the diet containing 6% red algae.