Background:When intestinal microbiota is imbalanced, a patient becomes more vulnerable to infectious complications; intervention with beneficial probiotics may help lower risk for infection. The aim of this study was to measure levels of inflammatory cytokine messenger RNA (mRNA) in surgical samples of intestinal mucosal tissues from patients who were given the probiotic Saccharomyces boulardii before undergoing colon surgery. Methods: Thirty-three patients undergoing colon resection were randomly assigned to receive at least 7-day preoperative probiotic treatment (n = 15) or conventional (n = 18) treatment. Probiotic treatment consisted of oral lyophilized S boulardii. Cytokine mRNA levels (interleukin [IL]–10, IL-1β, IL-23A, tumor necrosis factor [TNF]–α, IL-12B, interferon-γ [INF-γ], and IL-17A) were measured in samples obtained during the operation. Postoperative infections were also assessed. Results: Patients who received probiotics had significantly lower mucosal IL-1β, IL-10, and IL-23A mRNA levels than the control group (P = .001, P = .04, and P = .03, respectively). However, mRNA expression of other cytokines did not differ between the 2 groups (P > .05). The incidence of postoperative infectious complications was 13.3% and 38.8% in probiotic and control groups, respectively (P > .05). There was no perioperative mortality in either group. The mean total length of hospital stay was similar between the groups (P > .05). Conclusions: Probiotic treatment with S boulardii downregulates both pro- and anti-inflammatory cytokines in the intestinal colonic mucosa with no statistical impact on postoperative infection rates.