A novel method for the optical image e ncryption is presented,which is based on the wavelet packet transform (WPT) and fractional Fourier transform (FRFT).The idea of combining WPT with FRFT comes fr om the study of properties of them.Images can be decomposed by wavelet packet tr ansform.With the increase in the order of WPT,the image will be decomposed into more parts,of which each contains the essential information.Based on the good pr operty of WPT and the flexibility of FRFT,the method implicates encryption and d ecryption of the image and produces many keys,consisting of double random phase masks,the order of WPT and the order of FRFT.Meanwhile,the selected-image-encr yption in wavlet domain is realized in this paper,which varies the patterns of e ncryption.The method improves the security,and the ability of resisting maliciou s attacks is also enhanced.The encryption and decryption are implicated by numer ical simulation.The result of the simulation provides the requirement for analyz ing the properties of encryption and decryption.The feasibility and simplicity o f the method are verified by numerical simulation,and a simple optical implicati on of the method is also proposed.Based on the numerical simulation and theroy a nalysis,it can be confluded that the method for the optical image encryption is novel and effective.