Degradation of chlorobenzene in aqueous solution using a recycle ultrasonic reactor was investigated. The degradation rate constant increased with increasing volumetric now rates, reactor volumes and frequencies with electric power kept constant. Effective ultrasonic intensity was measured by a simple chemical dosimetry based on observation of the fading-time of alkaline phenolphthalein solution. The rate constant of the degradation reaction of chlorobenzene was proportional to the ultrasonic intensity D-ult [J/g] that is, a measure of the sonochemical effects. These results indicate that sonochemical effects can be interpreted in terms of the ultrasonic intensity or the ultrasonic energy consumed in the reactor.