Escherichia coli (E. coli) O157:H7 is an important cause of hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS). LPS-based vaccines need improvement since the anti-LPS antibodies raised by the vaccines are bactericidal and release toxin that may precipitate the development of HUS. Despite huge efforts, the treatment of infection with E. coli O157 has been difficult because antibiotics do not change the course of the enteritis caused by E. coli O157 and may increase the incidence of HUS through the release of Shiga-like toxin (Stx)-I. For this aim we tried the conjugate of E. coli O157 OSP bound to the nontoxic B subunit of Stx-I B as a vaccine that can induce both serum IgG anti-LPS antibody with bactericidal activity and neutralizing antibody to Stx-I. Mice were immunized s.c. with OSP-Stx-I B conjugate. Anti-sera were analyzed for the anti-LPS antibody, anti-Stx-I B antibody, complement-dependent bactericidal activity, and Stx-I neutralization activity. Mice injected with the bivalent conjugate elicited both bactericidal antibodies to E. coli O157 and neutralization antibodies to Stx-l. We also analyzed the distributional, functional changes of T lymphocytes in vitro and in vivo. After the injection of Stx-I, splenocytes showed a decrease in proliferation when stimulated with phytohemagglutinin (PHA) or LPS, and the number of $CD4^+$ and $CD^+$ T cells also decreased. Interleukin (IL)-2, IL-4 and IFN-$gamma$ productions by $CD3^+$ T cells were slightly increased in the Stx-I injected mice.