Abstract: Applications of male sterile was an important method for Chinese cabbage breeding, acquiring most of fertile related genes could provide clue for understanding the molecular mechanism of Chinese cabbage male sterile. cDNA-AFLP was used to found differentially expressed fragments from the fertile and sterile buds of AB01, an AB line of Chinese cabbage, RT-PCR and sequence alignment were used to deduce its function. A differentially expressed fragment, named as BRLSP-55, was found by cDNA-AFLP. This fragment was just expressed in fertile buds, but no signal was found in sterile one. The difference was verified by RT-PCR. The fragment was deduced to be a thionin protein, because it was mostly similar to thionine (Thionin Protein) of A. thaliana. The fertile related gene, BRLSP-55 should be a thionin protein, which plays a key role in sterile mechanism of Chinese cabbage.