In order to improve the mechanical properties of chitosan/zein composite film, chitosan solution was mixed with zein. Oleic acid (0%, 15%, 30%, 45% (w/w)) as plasticizer was added to the mixture. The particle size, zeta potential, static and dynamic rheological properties of the blend solution were analyzed. Then the effects of oleic acid on the barrier properties, mechanical properties and compatibility of the film were evaluated. The results showed that the particle size of the blend solution increased due to the addition of oleic acid. Compared with other treatments, the dispersivity of particle was better in the solution with 30% oleic acid. The value of PDI was 0.34 and particle size was 1307.5nm. With the increase of oleic acid content, the viscosity of blend solution decreased and the flow index increased. Elastic modulus and viscosity modulus of the solution increased. The mechanical properties of OA-30 film were improved. The tensile strength was up to 36.37 MPa, and the fracture elongation was up to 22.32% The barrier of membrane was enhanced. The water vapor transmittance and oxygen transmittance was reduced by 44.21% and 66.52%. OA-30 film was flat, and the chitosan and zein molecules had good compatibility. In summary, oleic acid modification improved the properties of chitosan/zein composite film.