A CW Gaussian beam illuminates a thin film of chemically enhanced bacteriorhodopsin (bR),and then strong self defocusing of the Gaussian beam passing the bR film will be shown when the ilumination intensity is greater than 220 W/cm 2 for the sample used.Owing to this effect,the self shaping of Gasussian beam can be realized.The analyses show the incident beam intensity and the thickness and concentration of the bR film influence the transverse profile of the transmitted beam.