To improve the utilization of fish processing by-products, fish oils were extracted from hoki, yellowfin sole, mackerel, and horse mackerel, and their compositions were examined. The proximate compositions obtained for these 4 species of by-product revealed they were composed of 68.1$sim$78.1% moisture, 1.2$sim$1.6% ash, and 13.8$sim$18.8% protein. Fish oils extracted from the hoki, yellowfin sole, mackerel, and horse mackerel were 5.5, 9.4, 13.4, and 10.3%, respectively. The total lipids extracted from the by-products of the 4 species were 6.21, 10.43, 12.81 and 10.06%, of which neutral lipids accounted for 77.38, 77.46, 87.21 and 86.79%, respectively. Neutral lipid analysis by TLC showed that triacylglycerol was the major component, while 1,3- and 1,2-diacylglycerols, free fatty acids, free sterols, and sterol esters were present as minor components. The major fatty acids were palmitic acid, stearic acid, and oleic acid. DHA and EPA were contained at levels of 0.2$sim$4.7% and 3.7$sim$9.5%, respectively, in the 4 types of fish oil. The fish oils extracted from the dark muscle fish, mackerel and horse mackerel, had greater polyunsaturated fatty acid (PUFA) contents than those of the white muscle fish species, hoki and yellowfin sole.