Abstract: To investigate the reason why Octopus vulgaris refuses to eat fish after having been fed with fish for a few days,the time when O.vulgaris stopped feeding Decapterus maruadsi was observed.The composition of amino acid and fatty acid of digestive gland of O.vulgaris of the experimental groups having been fed with D.maruadsi and C.acuta, and the control group of wild captured O.vulgaris was determined.The results showed that the contents of threonine,isoleucine,phenylalanine,aspartic acid,serine,tyrosine,histidine,and proline of the D.maruadsi feeding group were significantly lower than those of the control group,and the contents of valine,leucine,glycine,alanine,cystine,arginine,and the total contents of non-essential amino acidsof the D.maruadsi feeding group were significantly lower than that of the control group.The contents of valine,isoleucine,leucine,phenylalanine,lysine,glycine,and alanine of the C.acuta feeding group were significantly lower than that of the control group.Meanwhile,the total content of essential amino acids of the two experimental groups was significantly lower than of the control group.The tyrosine of the D.maruadsi feeding group was significantly lower than that of the C.acuta feeding group.C14∶0,C18∶3n3c and C22∶6n3c of the D.maruadsi feeding group were significantly higher than those of the control group,C18∶0,C20∶0,C22∶0,C18∶1n9c and C20∶4n6c were significantly lower than those of the control group.The total of monounsaturated fatty acids were significantly lower than those of the control group.C14∶0,C16∶0 and the total of saturated fatty acids were significantly higher than those of the C.acuta feeding group.C18∶0 of the C.acuta feeding group were significantly lower than those of the control group.C22∶0 and C18∶1n9c of the C.acuta feeding group were significantly lower than those of the control group.C18∶3n3c and C20∶3n6c were significantly higher than the control group,while C20∶5n3c and C22∶6n3c were significantly higher than the control group.C14∶0,C16∶0,and the total contents of saturated fatty acids of the D.maruadsi feeding group were significantly higher than that of the C.acuta feeding group.The above results showed that the reason why O.vulgaris refuses to eat fish after having been fed with fish for a few days was not caused by the composition of amino acids rather than the content of saturated fatty acids in the feed.The experimental results provided some necessary data for the study of O.vulgaris artificial diets.