BACKGROUND: Severity in irritable bowel syndrome (IBS) is associated to impaired quality of life and fatigue. Fecal microbiota transplantation (FMT) induces significant relief in gastro-intestinal related complaints. The objective was to evaluate the effect of FMT on the secondary endpoints: IBS-related quality of life and fatigue in patients with non-constipated IBS. METHOD: In this double-blind randomized placebo-controlled, parallel-group, single-center study, we enrolled patients with non-constipated IBS, defined by the ROME 3 criteria. We randomly assigned participants (2:1) in blocks of six to active or placebo FMT. Responder in fatigue and quality of life were defined as a decrease of 20 points in total Fatigue Impact Scale score, and improvement of 14 points in the IBS-quality of life questionnaire, respectively. In a modified-intention-to-treat population, we excluded participants who did not undergo treatment or who were diagnosed with any other disease by pinch biopsies during the treatment procedure. FINDINGS: Between Jan1, and Oct 30, 2015, we recruited 90 participants and randomly assigned them to active treatment (n = 60) or placebo (n = 30). Three participants did not undergo FMT and four were excluded after diagnosis of microscopic colitis, leaving 83 for final modified intention-to-treat analysis (55 in the active treatment group and 28 in the placebo group). Significant improvement in QoL (Odds ratio (OR) 3,801; confidence interval (CI) = 1,309-11,042 p = 0.011) and fatigue (OR = 4,398; CI = 1,175-16,468 and p = 0,020) was found at six months. Absence of other self reported functional disorders and presence of depression at baseline is suggested to predict a lasting effect of FMT in QoL and fatigue, respectively. INTERPRETATION: FMT induced significant relief in quality of life and fatigue. Results suggest a lasting effect of FMT in subgroups that should be further investigated in future studies. Funding Helse Nord, Norway and the Norwegian Centre of Rural Medicine, University of Tromsø, Norway.