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Ciprofloxacin (CIP) is a broad spectrum synthetic antibiotic drug of fluoroquinolones class. CIP can act as a bidentate ligand forming iron complexes during its degradation in the photo-Fenton process (PFP). This work investigates on PFP for the degradation of CIP to understand the formation mechanism and stability of iron complexes under ultraviolet (UV)-light illumination. A comparison was made with the UV-photocatalysis (UV/TiO2) process where CIP doesn’t form a complex. In PFP, the optimal dose of Fe2+andH2O2were found to be 1.25and 10 mmol/L with pH of 3.5. An optimal TiO2 dose of 1.25 g/L was determined in the UV/TiO2 process. Maximum CIP removal and mineralization efficiency of 93.1％ and 47.3％ were obtained in PFP against 69.7％ and 27.6％ in the UV/TiO2 process. The mass spectra could identify seventeen intermediate products including iron-CIP complexes in PFP, and only seven intermediate products were found in the UV/TiO2 process with a majority of common products in both the processes. The proposed mechanism supported by the mass spectra bridged the routes of CIP cleavage in the PFP and UV/TiO2 process, and the decomposition pathway of Fe3+-CIP chelate complexes in PFP was also elucidated. Both in PFP and UV/TiO2 processes, the target site of HO? radical attack was the secondary-N atom present in the piperazine ring of the CIP molecule. The death of Escherichia coli bacteria was 55.7％ and 66.8％ in comparison to the control media after 45 min of treatment in PFP and UV/TiO2 process, respectively.