Lethal toxicity of Nanhai crude oil, No. 0 fuel o il and No. 20 fuel oil to 3 species of larval shrimps, 4 species of larval f ishes and 4 species of shellf ishes was measured by controlled oil exposure experiments. The results show that the toxicity of the oils is in the order of No. 0 fuel oil > No. 20 fuel oil > Nanhai crude oil for both larval f ishes and larval shrimps, while toxicity order for the 3 species of shellfishes except Meretrix meretrix is No. 0 fuel oil > Nanhai crude oil. The dispersed Nanhai crude oil and No. 0 fuel oil are more toxic than their water soluble fractions. Among the 3 species of larval shrimps, Metapenaeus ensis is the most sensitive species to both No. 0 fuel oil and No. 20 fuel oil, while Penaeus japonicus is the most sensitive species to Nanhai crude oil. To lerance order of the larval f ishes to the 3 kinds of oils is Sparus latus > Mugil ophuyseni > Sparus macrocephalus, while the most sensit ive species to No. 0 fuel oil is Lateolabrax japonicus. Tolerance order of the shellfishes to No. 0 fuel oil and Nanhai crude oil is Meretrix meretrix > Paphia undulata > Scapharca subcrenata > Mytilus smaragdimus. In general, tolerance order of the exposured organisms to the o ils is shellfishes > fishes > shrimps.