This experiment was conducted to investigate the requirement of n-3 highly unsaturated fatty acids (n-3HUFA) for larval swimming crab Portunus trituberculatus. Three experiments were carried out in 1 l beakers, each holding 30 larvae. Larval swimming crab were fed rotifer cultured on freshwater chlorella Chlorella vulgaris, or fortified with corn oil, on enriched with various levels of either emulsified oil (EPA28G oil) containing 25.0% eicosapentaenoic acid (EPA) and 10.1% docosahexaenoic acid (DHA) or ethyl ester of EPA (purity about 92%). Larvae fed the rotifer cultured with Chlorella vulgaris or enriched with corn oil were hard to reach the first crab stage, indicating that perhaps both linoleic acid and linolenic acid in rotifer were not the essential fatty acids for the swimming crab. On the other hand, when larvae received the rotifer enriched with EPA28G oil or ethyl ester of EPA, the survival rate increased corresponding to the n-3 HUFA level in rotifer. On the basis of the feed performance and fatty acid compositions of rotifer, the suitable level of n-3HUFA , as provisions in rotifer, for larval swimming crab was 0.9-1.7 g/100 g dry basis.