Laser flash photolysis studies have been carried out to investigate the reactions of ciprofloxacin (CPX) with 2′-deoxyguanosine-5′-monophosphate (dGMP), N, N, N′, N′-tetramethyl-p-phenylenediamine (TMPD) and ferulic acid (FCA) in neutral aqueous solutions, respectively. CPX triplet state (3CPX*) can be quenched by TMPD, FCA and dGMP, with rate constants of 1.8 × 109, 1.5 × 109 and 5.8 × 107 dm3 mol−1 s−1, respectively. TMPD radical cation (TMPD·+) and FCA radical cation (FCA·+) were observed directly. The formation rate of CPX radical anion (CPX·−) was determined to be 1.5 × 109 dm3 mol−1 s−1. Redox reaction of dGMP was investigated through competing reactions using TMPD and FCA as probe. The triplet energy of CPX was determined to be 262 kJ mol−1. Electron transfer from TMPD, FCA and dGMP to 3CPX* was proposed.