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^* value 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.There′s no significant influence on tilapia L^* and b^*during storage.Variation of a^* value is in accordance with the content of CO residues. The a^* value 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.