Background: the wear of a removable partial prosthesis induces a quantitative and qualitative change in the oral microbiota. It influences oral physiology and often creates a new oral ecosystem. The aim of this study was to investigate the effect of wearing partial removable denture on the oral flora. Materials and Methods: a group of patients wearing removable partial dentures was included in the study .Samples of unstimulated saliva were collected from the patients’ mouth. The sampling was done in two times: before the wear of the partial denture and after one year of prosthetic wear. Colony count and identification of microorganisms were done. Data were analysed using the Statistical Package For Social Sciences (SPSS 22.0). A P-value ≤ 0.05 was considered significant. Results: Twenty-three patients without a history of wearing dentures were included in this study, of whom 16 (70%) were males and seven (30%) were females. The age of the patients ranged from 47 to 71 years with a mean age of 60.8 years. The oral rinse technique was used to collect the unstimulated saliva sample before (T0) and one year after the prosthesis wear (T1). Biological examinations showed qualitative and quantitative changes in the oral microbiota. In particular, Gram+ Cocci increased unlike Gram- Cocci which showed a significant decrease after denture insertion. Additionally, Bacilli and yeasts increased significantly after one year of denture wearing. Conclusions: The present study showed that the oral ecology can undergo changes after the insertion of a removable prosthesis. Further studies with a larger sample size are required in order to more precisely determine the effects of denture use on the oral microbiota.