The codA gene for choline oxidase, which converts choline into betaine. This enzyme, cloned from a soil bacterium Arthrobactor globiformis, has been transferred and expressed in tobacco by the Agrobatcterium-method transformation through the binary plasmid pGAH/codA. The pGAH/codA carried with Km(R) and Hyg(R),and coding sequence for a transit peptide from Rubisco small subunit gene (rbcS) was inserted between 35 S promoter and codA, so that the COD could be introduced into the chloroplast by this transit peptide. The transformed plants were screened on the medium containing the Km and Hyg. PCR, Western and gold immunolocalization tests showed that the codA gene has integrated into the tobacco DNA genome and its protein was expressed and the mature peptide has gone into the chloroplasts by the transit peptide. The results of salt-tolerance measuring for transgenic plants showed that the transgenic plants were more tolerance to the salt than the control plants. The young transgenic plants (1.0--1.5 cm) could survive at 400 mmol/L NaCl MS medium for more than 30 days. From them the higher tolerance plant T4-400 was obtained, which could grow at the 300 mmol/L NaCl MS medium well. The transgenic plants (6--8cm) could grow normally at the 400 mmol/L NaCl MS medium while wild plants failed to do so. So the transferred plant with codA enhanced its tolerance to the salt stress.