Background: Intestinal inflammation and oxidative stress contribute to the pathophysiology of irritable bowel syndrome (IBS). This clinical trial investigated the effects of a probiotic supplementation on symptom severity and quality of life (QOL) in IBS patients. Methods: Forty-six IBS patients were randomised to receive either a multi-species probiotic or placebo for 8 weeks. Clinical symptoms were evaluated using the IBS Severity Scoring System (IBS-SSS) and IBS QOL questionnaire. Serum levels of IFN-gamma, IL-1beta, IL-10, IL-6, malondialdehyde (MDA), total antioxidant capacity (TAC), and nitric oxide (NO) were measured before and after the intervention. Results: After 8 weeks, the probiotic group showed significant improvements in QOL scores, and reductions in IBS-SSS and MDA levels compared to placebo group. TAC levels were significantly higher in probiotic group. However, no significant differences were observed in cytokine or NO levels. Conclusions: This multi-species probiotic supplement was safe and effective in reducing symptom severity and improved QOL of IBS patients.