To analyze the localization of attenuated Salmonella typhimurium after oral immunization. Prokaryotic expression plasmid pYA33-DsRed, carrying the RFP gene, was constructed and electro-transformed into an attenuated strain X4550 of Salmonella typhimurium, the recombinant bacteria were named as X4550 (33-DsRed). The macrophage cell line RAW264.7 and bone marrow dendritic cell (BMDC) were invaded by X4550 (33-DsRed) in vitro. Furthermore, BALB/c mice were immunized with recombinant bacteria orally. RFP positive cells (RFP+ cells) were detected by Flow Cytometry (FCM) from spleen, liver, Mesenteric lymp node (MLN), Peyer's patch (PP), Inguinal lymph node (ILN). The invasion rate increased when the multiplicity of infection(MOI) were improved in this two kinds of cells respectively. After oral immunization with X4550 (33-DsRed), RFP+ cells were detected by FCM on 1d, 2d, 3d, 5d, 7d in spleen, liver, MLN, PP, ILN cells. The first day, RFP+ cells were detected in MLN and PP, and in PP at a higher rate of 1.4% than that of MLN. 0.4% RFP+ cells were detected the next day in ILN. On 3th day, the rates of RFP+ cells were increased in all of above tissues or organs and decreased on the 5th day. At the 7th day, RFP+ cells couldn't be detected in all tissues or organs tested. It is suggested that the invasion ability and the transfer through mucosal pathway and targeting to recognize immune tissue or organs are favor of the research in mucosal vaccine and the vaccine efficiency.