Abstract: We studied the effect of carbon monoxide(CO) color retention on color of tilapia dark muscle during storage. The result shows that red value a* of product could be improved significantly and retained in a high level during storage.The a* of tilapia treated with CO increases in the first few days and then decreases slowly during cold storage, while a* of untreated ones declines slowly all the way. Color of fillets can be retained within 13 d in cold storage and half year in frozen storage. Theres no significant influence on tilapia L* and b*during storage. Variation of a* value is in accordance with the content of CO residues.Thea* of fillets treated with CO usually continue increasing after storage for 1~2 d，especially during cold storage. The formation of CO-myoglobin(CO-Mb) plays important role in preventing Mb from oxidation.