Gut microbiota is involved in numerous physiopathological situations including cancers. Our objective is to evaluate the relationship between the composition of microbiota and the clinicobiological characteristics of patients with breast cancer. Clinical data and faeces from 32 patients with early stage breast cancer were collected, before any therapeutic intervention. Bacterial DNA extracted from faeces was amplified by PCR targeting 16S rRNA gene sequences specific to different bacterial phyla. Expression was compared in groups of patients defined by clinical stages of the disease as well as BMI. Most patients suffered of invasive ductal (81%), clinical stage 0 (46.9%), with histological grading II (62.5 %), ER/PgR (80%) and HER2 (15%). About 28.1 % and 12.5 % of patients were overweight and/or obese, respectively. Significant differences were observed for absolute numbers of total bacteria and for some studied bacterial groups (F prausnitzii, Firmicutes, Blautia and Egerthella) according to BMI. Compared with patients with grade I (n=5), patients with grade III (n=7) had increased absolute numbers of Blautia sp. (9.8±0.2 vs 9.5 ± 0.2 log copies.g-1, p=0.048), for example. Furthermore, absolute numbers of Bifidobacterium and Blautia, and proportions of F Prausnitzii and Blautia, were significanly different according to clinical stages. Our study highlighted that, in these patients, intestinal microbiota composition differs according to clinical characteristics and BMI. These results should be confirmed to clarify the link between breast cancer and intestinal microbiota.