Faecal microbiota transplantation (FMT) may contribute towards disease remission in ulcerative colitis (UC), but it is unknown which factors determine long-term effect of treatment. Here, we aimed to identify bacterial signatures associated with sustained remission. To this end, samples from healthy donors and UC patients—grouped into responders and non-responders at a primary end point (week 12) and further stratified by sustained clinical remission and relapse assessed at ⩾1-year follow-up were analysed, comparing the efficacy of FMT from either a healthy donor or autologous faeces. Microbiota composition was determined with a 16S rRNA gene-based phylogenetic microarray on faecal and mucosal samples, and functional profiles were predicted using PICRUSt with quantitative PCR verification of the butyrate production capacity; short-chain fatty acids were measured in faecal samples. At baseline, UC patients showed reduced amounts of bacterial groups from the Clostridium cluster XIVa, and significantly higher levels of Bacteroidetes as compared with donors. These differences were reduced after FMT mostly in responders. Sustained remission was associated with known butyrate producers and overall increased butyrate production capacity, while relapse was associated with Proteobacteria and Bacteroidetes. Ruminococcus gnavus was found at high levels in donors of failed FMT. A microbial ecosystem rich in Bacteroidetes and Proteobacteria and low in Clostridium clusters IV and XIVa observed in UC patients after FMT was predictive of poor sustained response, unless modified with a donor microbiota rich in specific members from the Clostridium clusters IV and XIVa. Additionally, sustained response was associated with restoration of the butyrate production capacity.The ISME Journal advance online publication, 11 April 2017; doi:10.1038/ismej.2017.44.