The chemical composition and antioxidative activity of mungoong, a shrimp extract paste from the cephalothorax of white shrimp (Litopenaeus vannamei), were studied. Mungoong contained 42.3% polyunsaturated and 29.59% saturated fatty acid. It was rich in C20:5 n-3 (eicosapentaenoic acid) (4.31 g/100 g) and C22:6 n-3 (docosahexaenoic acid) (7.07 g/100 g). Mungoong consisted of Na (15.3 g/kg) and Ca (8.07 g/kg) as the major minerals. Fe and Cu were found at very low content. Glutamine was the most abundant amino acid, while lysine, alanine and asparagine were predominant in mungoong. Mungoong water extract at a level of 1,000 ppm exhibited antioxidative activity in a β-carotene–linoleic acid, lecithin liposome and comminuted fish model system. Antioxidative potential determined by 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) and 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activities and ferric-reducing antioxidant power was quite stable during 8 weeks of storage at 4C and room temperature (28–30C). Antioxidative activities determined by all assays remained constant within the first week (P > 0.05). Thereafter, only slight decreases in activities were noticeable. During storage at both temperatures, mungoong's 2-thiobarbituric acid (TBA) values increased during the first 2 weeks of storage (P < 0.05), followed by the gradual decrease of 8 weeks. Nevertheless, no marked changes in TBA values were observed between samples kept at both storage temperatures. Thus, antioxidative peptides might contribute to the retardation of lipid oxidation of mungoong during the extended storage.