Reunion Island (21.0°S, 55.5°E) is a French and European territory situated in the Indian Ocean in the tropics where solar ultraviolet radiation (UVR) levels are high almost all-year round. This is mainly due to intense incident solar radiation combined with weak stratospheric ozone columns. Yet, very few UVR and ozone measurements are available or operational in these regions, especially in the southwest Indian Ocean countries. Since 2009, the Reunion University, a French and European university, started a research program based on ground-based solar UVR and ozone observations. Continuous UVR measurements require instrument monitoring and calibration processes in terms of wavelength and intensity on regular intervals and made with regular comparison against a reference instrument. Several UV instruments comparison has already been done [1], but a comparison at high UV level can highlight a different instrument trend. In the framework of the NDACC (Network for the Detection of Atmospheric Composition Change) and in collaboration with the LOA (Laboratoire d'Optique Atmosphérique, University of Lille, France) a Bentham DM300 spectrometer (BT) is operated at Reunion Island. We recently implemented an inter-comparison campaign between the Bentham spectroradiometer and four UV radiometers: a Kipp&Zonen UVS-E-T (KZ), a Solar Light 501 (SL), a SGlux UV COS (SG) and a Davis radiometer (DV), with the Bentham spectrometer as a reference. It should be noted that the Kipp&Zonen and Solar Light 501 radiometers were calibrated during the International UV filter Radiometer Comparison in summer 2017 organised by PMOD/WRC at the WCC-UV in Davos [2]. In order to identify clear sky conditions, an all-sky camera recording cloud fraction (CF) has been operating at the observation site.