A novel cathodic electrochemiluminescence (ECL) behavior of the norfloxacin (NFLX)/peroxydisulfate (S 2 O 8 2− ) system in purely aqueous solution at a glassy carbon electrode (GCE) was firstly reported in this paper. The NFLX/S 2 O 8 2− system could produce a very strong ECL signal under the potential scan from 0 to −1.8V in 0.1M phosphate buffer solution (pH 7.0) containing 0.24mg/mL NFLX and 10mM S 2 O 8 2− , which was about 350 times higher than that of S 2 O 8 2− alone, while NFLX did not produce ECL in the absence of S 2 O 8 2− . The effects of pH value, S 2 O 8 2− and NFLX concentration on the ECL intensity were investigated and the possible mechanism for the ECL behavior of NFLX/S 2 O 8 2− system was proposed.