Effects of host immunization on bacterial translocation and growth performance in weanling piglets were studied. Twenty four barrows were assigned to one of two immunization treatments: Control group (CON: immunized with placebo) or Immunization group [IMMU: immunized with Antigen cocktail; Keyhole limpet hemocyanin (KLH), Ovalbumin (OA), and Tetanus toxoid (TT)]. On d0, piglets were weaned and intramuscularly immunized with 2 ml of placebo or Antigen cocktail, respectively. Antigen-specific Ig titers were determined by ELISA (Enzyme Linked ImmunoSorbent Assay). Ig titers to E. coli-derived lipopolysaccharides (LPS) were measured as the indicator of bacterial translocation. Ig titers to LPS were higher (p<0.10, 0.05 or 0.01) in CON group before immunization (d0), but the difference disappeared with time and IgA titers to LPS became higher (p<0.05) in IMMU group on d39. In IMMU group, IgG titers to LPS from d28 onwards showed positive correlations (p<0.10, 0.05, 0.01 or 0.001) with IgG titers to KLH from d11 onwards and with IgM titers to KLH from d7 onwards. Generally, growth performance was negatively related to IgG titers to LPS. Average daily gain for d28 to d35 showed negative correlations (p<0.10, 0.05, or 0.01) with IgG titers to LPS on d28 onwards in immunization group. These results reveal some evidences that host immunization might facilitate bacterial translocation and high humoral immune responses to LPS are negatively related with the growth performance.