Melanosis, microbiological, chemical, and physical changes of Pacific white shrimp (Litopenaeus vannamei) treated with catechin were monitored during iced storage of 10 days. Whole shrimp treated with catechin solution (0.05 or 0.1%) had retarded growth of psychrophilic bacteria and spoilage microorganisms including H(2)S-producing bacteria and enterobacteriaceae throughout storage in comparison with the control and those treated with 1.25% sodium metabisilfite (SMS) (P < 0.05). The lower increases in pH and total volatile base (TVB) content were obtained in the shrimp treated with catechin solution at both levels, compared with those of other samples (P < 0.05). Lipid oxidation, loss in freshness and melanosis were lowered by catechin treatment. In general, the efficacy of catechin in lowering melanosis and quality losses increased with increasing levels used. Additionally, catechin (0.01, 0.05, and 0.1% (w/v)) showed inhibitory activity toward polyphenoloxidase (PPO) of Pacific white shrimp in a dose-dependent manner. Therefore, catechin can be used as a promising melanosis inhibitor as well as an antimicrobial and an antioxidant in ice-stored shrimp.