The aim of this study was to screen the antimicrobial and acaricidal activity of 20 endemic or indigenous plants from Reunion Island (Indian Ocean). Plants were chosen on the basis of their traditional uses and their biocidal activities found in the literature. A survey was conducted in the local population to assess and supplement knowledge about the selected plants. The collected information confirmed and/or supplemented the data obtained for nine plants. Seven plants were described for the first time for their traditional uses in medicine and ethnoveterinary practices. To evaluate their biocidal activities, leaves or bark were treated with ethyl acetate using an accelerated solvent extraction method. Six bacteria and five fungi, frequently implicated in infectious diseases, were used to assess the antimicrobial activity of these extracts. A preliminary screening using the paper disk diffusion assay showed an effective antibacterial activity of 16 extracts. The minimum inhibitory concentration (MIC) of active plant extracts was then determined using a microdilution method. The leaf extract from Peperomia borbonensis displayed the widest spectrum of antibacterial activity and was the only one to act as a fungicide. In parallel, acaricidal bioassays were performed on the larvae of the tick Rhipicephalus microplus (Ixodidae), and plant extracts from Peperomia borbonensis and Zanthoxylum heterophyllum were the most effective. The preliminary studies of these plant extracts exhibited biocidal activities that were not described in the literature and that are congruent with traditional uses for some of them. Investigations are currently being conducted to isolate the active compound(s) and evaluate their potential for future developments and applications.