Abstract: The aims were to investigate the structure and function of Brassica rapa defensin genes. According to the sequence of Brassica rapa defensin genes, 4 Brassica napus defensin genes were cloned by polymerase chain reaction (PCR) and predicted by bioinformatic methods. The results showed that the cDNA sequence was 325-335 bp, and the open reading frame (ORF) was 231-243 bp which could encode a polypeptide of 78-80 amino acids. Brassica napus defensin genes resulted in significant differences in the long evolutionary process, resulting in significant differences, but the 6-8 conservative cysteine residues are stable. Phylogenetic tree showed that Bndef1, Bndef2, Bndef3 had close genetic relationship with Raphanus sativus Rs-AFP1 and Orychophragmus violaceus Omdef, Bndef4 had close genetic relationship with Vigna unguiculata Vudef. The Brassica napus defensin genes defensin proteins were stable protein with a signal peptide structure, which might be secreted protein.