Sulfate radical (SO4rad-)-based advanced oxidation processes (SR-AOPs) are promising technologies for organic micropollutant removal. In this study, medium pressure (MP) UV was used to activate peroxymonosulfate (PMS) as an emerging SR-AOP for the degradation of ciprofloxacin (CIP), which is a typical fluoroquinolone. It was found that similar to 80% of CIP was removed at a UV dose of 200 mJ/cm(2) in the MPUV/PMS system (3.02 mu M CIP, 0.2mM PMS, pH=3.75). Scavenging experiments indicated that both hydroxyl radical (radOH) and SO4rad- contributed to CIP removal in the MPUV/PMS system. In acidic conditions, the predominant reactive radical was SO4rad-, while the role of radOH in CIP degradation was enhanced under neutral and alkaline conditions. A high PMS dose, high pH, low CIP concentration and the presence of Cl-, CO32- and NO3- promoted CIP removal. Transformation products (TPs) of CIP were detected in the MPUV-only and MPUV/PMS experiments, and the initial transformation pathways were proposed. Defluorination and transformation of the piperazine ring were found to be the main pathways for degrading CIP during MPUV-only and the MPUV/PMS processes, respectively. An umu test indicated that MPUV/PMS was effective at reducing the genotoxicity of CIP solutions, but the MPUV-only was not. However, some TPs formed during the initial oxidation period in the MPUV/PMS system had equivalent and even higher toxicity than CIP. The results of this study contribute to our understanding of CIP degradation by MPUV/PMS and provide some basic information for use in future studies and applications.