Fish oil is considered as a great nutritional importance due to a high content of essential n-3 polyunsaturated fatty acids (PUFAs) such as linolenic acid, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA). However, PUFAs are susceptible to oxidative deterioration. Methanolic extract of Java plum seed was a source of strong antioxidant polyphenols against DPPH as well as strong Ferric (Fe3+) reducing agent. The aim of the research was to evaluate the effect of methanolic extract of Java Plum seed (MEJS) on lipid oxidation of fish oil from striped catfish (Pangasius hypothalamus) in oil-in-water emulsions as a food model at 35±2ºC during 144 h of storage. The results showed that MEJS has stronger inhibition activity than Grape Seed Extract (GSE) but lower than BHA (p<0.05) according to conjugated dienes (CD), peroxide values (PoV), and thiobarbituric acid reactive substances (TBARS). Inhibition activity of MEJS on lipid oxidation ranged between 28% and 38% at concentrations of 50-800 mg/L during 144 h of storage.