In order to detect the antimicrobial mechanism of the combination of cinnamon oil and gamma irradiation,the roles of them on the cell fatty acid and protein characteristics of Shewanella putrefaciens and the cinnamaldehyde change in S.putrefaciens were evaluated.Cinnamaldehyde was the main component of cinnamon oil,accounted for 78.54%.There was no obvious increase of cinnamaldehyde concentration in S.putrefaciens after treatments.The cinnamaldehyde in nutrient broth was transformed to cinnamyl alcohol with the role of S.putrefaciens.However,no obvious cinnamyl alcohol was observed in S.putrefaciens.No matter irradiation or cinnamon oil had a significant effect on fatty acids (p<0.05).The SDS-PAGE analysis showed that the effect of gamma irradiation on the outer membrane proteins (OMP) was not significant,but higher concentration of cinnamon oil and the combination of them can affect the OMP subunits significantly.These findings indicated that the antimicrobial role of the combination of cinnamon essential oil and gamma irradiation is mainly on the membrane of S.putrefaciens.