An efficient transformation system for Chinese cabbage cotyledon explants was developed using Agrobacterium tumefaciens strains LBA4404 harbouring the plasmid pMOG411 and the plasmid pBin Omega SCK respectively. Various factors affecting the transformation efficiency and subsequent regeneration were identified. The age of seedlings, growth conditions and status of Agrobacterium suspension, preculture of explants, cocultivation time, ratio between Agrobacterium and explants, acetosyringone and concentration of kanamycin had a significant influence on transformation frequency and plant regeneration. The presences of the antibacterial peptide gene and the cowpea trypsin inhibitor gene in those selected shoots in kanamycin medium were confirmed by PCR, Southern blotting and Northern blotting, The frequency of regeneration from cotyledons was analyzed in eight parental lines of Chinese cabbage and five lines were suitable for obtaining transformed plants, among which Qingmaye C and Qingmaye D were more responsive than other lines.