Pyrazolone pharmaceuticals such as isopropylphenazone (PRP) and aminopyrine (AMP) were commonly used as antipyretic analgesics, and their frequently detection in aquatic environment has become a major concern in recent years. Chlorine dioxide (ClO2) disinfection process has been proved to be a feasible way to degrade antipyrine (ANT), which is the first synthetic pyrazolone pharmaceutical. In this work, the reaction kinetics, degradation pathways and genetic toxicity of PRP and AMP during ClO2 disinfection process were investigated. Experimental results demonstrated that the reaction of both PRP and AMP with ClO2 followed second-order kinetics, the second-order rate constants were calculated to be k(app)(PRP)= 11.0 M-1 s(-1) and k(app)(AMP)= 1.30 x 10(5) M-1 s(-1) at neutral pH. Slightly alkaline environment (pH = 9) was in favor of the reaction. C=C double bond and C-N bond on pyrazolone ring were main active groups under ClO2 electrophilic attack. The degradation pathways of pyrazolone pharmaceuticals could be concluded as C=C cleavage, ring-opening reaction and de-carbonyl reaction. Pyrazolone contaminated water exhibited genetic toxicity according to micronucleus test of Viciafaba root tip, however, the toxicity could be reduced through ClO2 disinfection process.