Background and Aim:Orangutans are an “umbrella species” for conserving tropical forests in Sumatra and Kalimantan. There are remarkable changes between the gut microbiomes of wild and captive Sumatran orangutans. This study aimed to profile gut microbiota of wild and captive Sumatran orangutans.Materials and Methods:Nine fecal samples collected from wild orangutans and nine fecal samples collected from captive orangutans were divided into three replicates. Each replicate randomly combined three pieces and were analyzed on the Illumina platform. A bioinformatics study of 16S rRNA according to Qiime2 (Version 2021.4) and microbiome profiling analysis was conducted.Results:The relative abundance of different microbial taxa varied significantly between wild and captive Sumatran orangutans. Among the operational taxonomic units, various proportions ofFirmicutes,Proteobacteria,Bacteroidetes,Euryarchaeota,Acidobacteria, ActinobacteriaandVerrucomicrobiapredominated.Solobacteriumwas found only in 19% of captive orangutans.Methanobrevibacterwas identified to be prevalent among wild orangutans (16%). Analysis of the core microbiome from the combined wild and captive data revealed seven species as cores. According to linear discriminant analysis effect size,Micrococcus luteus,Bacteroidescaccae,Lachnospiraceae bacterium,Ruthenibacterium lactatiformans,Haemophilus haemolyticus, andChishuiellaspp. were microbiome biomarkers in captive orangutans, whereasRoseburia inulinivorans,Collinsella aerofaciens,Oscillibacterspp., andEubacterium halliiwere microbiome biomarkers in wild orangutans.Conclusion:There were differences in the microbiome biomarkers of wild and captive Sumatran orangutans. This study is important for understanding the role of gut bacteria in the health of Sumatran orangutans.