This study was designed to evaluate the effects of hyperbaric oxygen (HBO 2 ) on intestinal microflora and bacterial translocation (BT) caused by experimentally induced thermal injury in rats. Rats were separated into four groups, namely, HBO 2 group, thermal injury (TI) group, TI + HBO 2 group, and control group. All groups were further separated into short-term (2 days) and long-term (7 days) treatment or injury groups. Control group was neither exposed to thermal injury nor was given any treatment. Thirty percent second-degree thermal burn was induced on the dorsal body part of the rats in TI groups. In the HBO 2 groups, rats received HBO 2 treatment either without TI or following TI induction, for 2 and 7 days, respectively. Sampling from tissues and portal vein was performed on day 3 in the short-term groups and on day 8 in the long-term groups. Samples were cultured for identification of bacteria and colony counts. HBO 2 treatment significantly reduced the colony counts of endogenous microflora in distal ileum of healthy rats ( p < .05), while TI significantly increased the colony counts of endogenous microflora in distal ileum in short and long-term TI groups ( p < .05). Presence of bacterial translocation was proven by bacterial isolation in mesenteric lymph nodes, liver, spleen and blood. Both short- and long-term HBO 2 treatment following TI significantly reduced the colony counts of intestinal microflora ( p < .05) and prevented bacterial translocation almost completely. It is concluded that thermal injury causes both bacterial overgrowth within intestinal lumen and bacterial translocation across the intestinal wall. HBO 2 administration prevents both bacterial overgrowth and translocation.