In order to obtain a new castor with low toxity,RNAi interference technology was used to regulate the expression of the RTA(ricin toxin A-subunit) gene.The RTA gene are amplified by Polymerase Chain Reaction technology,and then RTA transgenic expression vector(pBI-RTA-S-AS) was constracted successfully.Secondly,pBI121-RTA-dsRNA vector was transferred into cotyledonary node by Agrobacterium tumefaciens-mediated transformation.Transformed castor plants were identified by growth on medium containing 25mg/L Kanamycin and PCR.The results showed that 762 bp fragment was obtained.Three transformants were obtained and all of them were further identified as positive transgenitic plants by PCR.