An 8-week feeding trial was conducted to determine the optimal dietary soy lecithin requirement for juvenile swimming crabs (Portunus trituberculatus) reared in cement pools. Six iso-energetic and iso-lipidic experimental diets were formulated to contain graded levels of soy lecithin, which were supplemented with 0, 10 g/kg, 20 g/kg, 40 g/kg, 60 g/kg, 80 g/kg of soy lecithin respectively. The results indicated that when the dietary soy lecithin was from o to 40 g/kg, WR, MR, PER, SGR and MR were increased significantly, but FCR decreased significantly (P<0.05). The results indicated that optimal soy lecithin in the diet can improve growth performance and feed utilization for juvenile swimming crab. TP, TG and HDL concentration in serum was not affected by the dietary soy lecithin levels, but the contents of CHO and GLU were increased significantly with the soy lecithin increasing from 0 to 40 g/kg, but were not affected by the dietary soy lecithin increasing (P<0.05). The T-Aoc, MDA and LSZ activity in hepatopancreas were not affected by the dietary soy lecithin levels (P>0.05). When the dietary soy lecithin was 60 g/kg, the SOD activity in hepatopancreas was significantly higher than other diets (P<0.05). The content of GPX in hepatopancreas was increased significantly with the soy lecithin increasing from 0 to 40 g/kg, but was not significantly affected by the dietary soy lecithin increasing from 40 g/kg to 80 g/kg (P<0.05). With the soy lecithin supplementation, we also observed that the contents of DHA, EPA, C18:2 and n-3PUFA in muscle were not affected by the dietary soy lecithin (P>0.05), but DHA and EPA in hepatopancreas were significantly increased with the soy lecithin increasing from 0 to 40 g/kg (P<0.05), however they were not significantly affected by the soy lecithin increasing from 40 g/kg to 80 g/kg (P>0.05). With the soy lecithin increacing from 0 to 40 g/kg, the contents of C18:2 in hepatopancreas were very significantly decreased (P<0.01), but the contents of n-3PUFA in hepatopancreas were not significantly affected (P>0.05), while with the soy lecithin increasing from 40 g/kg to 80 g/kg, the contents of C18:2 in hepatopancreas were significantly increased (P<0.05), but the contents of n-3PUFA in hepatopancreas were very significantly decreased (P<0.01). The results showed that the soy lecithin in diet improved the content of n-3PUFA, DHA and EPA in hepatopancreas. Based on two slope broken-line model based on specific growth rate against dietary soy lecithin levels, the optimal dietary soy lecithin requirement was estimated at 41.96 g/kg for juvenile swimming crab.