It is currently supposed that gut microbiota dysbiosis may be a potential trigger for IBS, inducing most of the pathological conditions. Thus, the modulation of dysbiotic intestinal microbiota by biologically active biotics, including probiotics, prebiotics, and, when combined, synbiotics, is a promising treatment approach in IBS. Recent meta-analysis including 20 studies involving 3011 patients reported that probiotics are effective and safe for IBS patients; however, definite conclusions are challenging due to the high heterogeneity [1]. They also reported an unmet need for large-scale, well-designed, and rigorous trials to confirm their effectiveness in IBS [1]. The efficacy of probiotics in IBS also depends upon the type of strain selected for therapy. A systematic review and meta-analysis published in 2020 showed that single-strain formulations, particularly those containing Bifidobacterium or Lactobacillus strains, may be more effective in IBS patients [2]. There is evidence to suggest species/strain-specific effectiveness in IBS patients, which further underlines the role of proper selection of probiotics for the best approach according to patients’ specific needs [3]. As an effective treatment for IBS patients, spore-based Bacillus spp. probiotics have been reported in a recent study [4]. The safety and efficacy of Bacillus clausii UBBC-07 have been reported in multiple studies for diarrhea and oral mucositis [5-9]. However, the role of this single strain has not been reported in IBS patients. Therefore, we planned this study to explore the safety and efficacy of Bacillus clausii UBBC-07 in patients with IBS.