CryIAc protein of Bacillus thuringensis expressed in E.coli transformed with pQEBt was purified by Ni-NTA affinity chromotography. One phage (PH5) that binds specifically to Bt protein was selected from a combinatorial library of random 7-mer peptides fused to minor coat protein (pⅢ) gene of the filamentous coliphage M13 through three cycles of biopanning and ELISA analysis. A new method of recombination phage aided detection of insecticidal Bt protein in transgenic plants was developed using PH5. The phages selected should also be useful in the structure study of functional domains of Bt insecticidal proteins.