The present investigation describes the kinetics and the mechanism of the inhibiting action of chalcone on the rate of Ce(IV)-initiated polymerization of acrylonitrile in the temperature range 30–40°C. The effect of monomer, metal ion, chalcone, perchloric acid, acetic acid, sodium sulfate, and manganese sulfate on the rate of polymerization has been studied. The most striking observation in the present investigation was the rate mechanism. The plot of [M]/Rpversus 1/[M] gave a negative intercept which appears to be a general phenomenon for all inhibiting substrates. The activation parameters were calculated, and a suitable reaction scheme is proposed.