Abstract: An experimentation was conducted to determine the effect of the addition of laminarin in feed on the growth, body composition and immunity of pearl gentian groupers at an aquaculture farm.Four separate 30 m² concrete pools were used as a closed circulating water aquaculture system for the experiment. Simultaneously, approximately 1 800 groupers were placed in each of two pools for the treatment or control. The initial weight of the individual fish was (275.55±29.79) g. They were fed with either a control diet or one containing 0.6% laminarin in the pools for 66 d. At end of the feeding period, the weight gain of the groupers in the treatment group increased 29.03% (P < 0.05), the specific growth ratio increased 23.88% (P < 0.05), and the feed conversion rate decreased 15.20% (P < 0.05) over those of control, while the nutrient content in flesh of the treatment showed no significant difference as compared with control (P>0.05). For each kg weight gain on the fish, the cost of the treatment diet was 1.96 yuan less than that of control, i.e., a reduction of 12.54%. On the other hand, the activities of alkaline phosphatase, lysozyme and total superoxide dismutase enzymes of the groupers in the treatment group were significantly higher than those of control (P < 0.05). It was, thus, concluded that addition of 0.6% laminarin in the regular feed would improve the growth and enhance the immunity of pearl gentian groupers in aquaculture.