Measurements of total ozone over Greece have been performed with NILU-UV multi-channel radiometers since 2005. In this study, the measurements at two stations, Thessaloniki and Athens, of the ultraviolet (UV) monitoring network are compared with ozone values derived from Brewer spectroradiometers at the same sites. The overall percentage difference on daily averages (including measurements for solar zenith angle below 70 ) is below (1 3.5)% at both sites. The cloud modification factor (CMF), specified as the ratio of measured irradiance with a model-derived cloud-free value, is being used to examine the effect of cloudiness on the retrieved ozone abundances. During days with average CMF values above 0.7, the difference in total ozone measurements is within 5%. The use of momentary ozone values from the radiometers with this limitation in CMFreduces the difference of the average values to (0.0 2.2)% for Athens and (0.21 2.8)% for Thessaloniki.