This work assessed the significance of the taxonomic composition and/or metabolic activity of obese- microbiota by massive 16S rRNA gene sequencing of the faecal microbiome of obese and normoweight individuals. A total of 26 human faecal samples were analysed in this study. Faeces were collected from 13 normoweight (N) (body mass index = 18 - 25 kg m2) and 13 obese (O) adult volunteers (body mass index > 30 kg m2). All volunteers gave written informed consent to the protocol, which had been approved by the Clinical Ethics Committee of Hospital Ramón y Cajal with the code 394/14 and Spanish Council of Scientific Research (CSIC; Spain). Stool samples were collected under aseptic conditions in sterile and screw-top containers and immediately stored at –80°C. The taxonomic composition of the fecal microbiota of obese (Om) and normal weight (N) individuals was determined by massive sequencing using the Illumina Seq platform. Genomic DNA was extracted from faecal samples previously thawed at room temperature following the protocol described by Moles et al. (2013). DNA samples were subjected for massive 16S rDNA gene V3-V4 amplicon sequencing on the Ilumina MiqSeq platform. The primers were selected from previously described ones (Klindworth et al., 2013). Quality assessment was performed by the use of prinseq-lite program (Schmieder, et al., 2011) applying following parameters: min_length: 50; trim_qual_right: 30; trim_qual_type: mean; trim_qual_window:20; R1 and R2 from Illumina sequencing where joined using FLASH program (Magoc, et al., 2011) applying default parameters., We acknowledge financial support from the Spanish Ministry of Science and Innovation (AGL2016-75951-R)., Sequence Data: Trimmed and cleaned reads for each sample, according to parameters described in Methods section. When a sequence did not fit the minimum length or quality is removed from the dataset. This will generate a singleton file containing those reads without their pair.-- N denotes sequence data of faecal samples from normoweight individuals; OM denotes sequence data of faecal samples from obese individuals., Peer reviewed