In this study, the ethyl ester of EPA and DHA was produced, using the soapstock (soap lye and solid lipid) of fish oil as the raw material through acid catalysis and alkali catalysis, whose optimal conditions were investigated. It was obtained that the optimal conditions for acid catalysis (a) and alkali catalysis (b) were as follows: (a) refluxing for 4h at normal atmosphere, 80, phosphoric acid, 3%, [w/w], alcohol, 65%, [v/v]; (b) sodium hydroxide, 1% [w/w], alcohol, 40% [v/v], 50for 2-6h in the stirred autoclave. Under the optimal conditions, a conversion ratio of ethyl ester fish oil of 96.8% (a) and 97.4% (b) were obtained. The concentration of EPA and DHA was enhanced from 30% to 60.7% through three class molecular distillation method. This n-3 polyunsaturated fatty acid-enriched fish oil may be a valuable supplement in the green feed.