In order to find an alternative source for the highly unsaturated fatty acids oil with lower cost, a marine trash fish Odonus niger has been analysed and characterised. The body weight and the corresponding liver weight of the fish were studied and the results showed that for one gram increase in the size of the animal, the liver weight can increase to 0.04 g. The oil yielding capacity of the liver was assessed by four different methods namely Soxhlet, Bligh and Dyer, Direct steaming and Solar extraction. The percentage of oil yield was high in Soxhlet method (67.7%), but it was 54.3% in Bligh and Dyer method, 42.5% in direct steaming method and minimum of 32.0% in solar extraction method. The solidification point of all the extracted oils remained at 29 ± 0.5^o C. The specific gravity (0.95 to 0.96) and refractive index (1.42µ to 1.48µ) of the oil extracted by the four different methods were not varied significantly. The cholesterol contents of the oil extracted by Bligh and Dyer and direct steaming extraction methods were at the highest level (1991.00 and 2059.00mg 100ml^-1) but it was 50% less in other methods. The percentages of PUFA in the total fatty acid of the oils were 13.78, 20.46, 19.07 and 22.54% (by weight) in solar extraction, direct steaming, Soxhlet and Bligh and Dyer methods, respectively. Thus t he physico-chemical properties of liver oil of O. niger were found to be influenced by the extraction adopted methods. Also it is clear that Bligh & Dyer method is the suitable method for the extraction of liver oil from marine fishes without much loss of nutrients.