The enhancement of sonochemical-reaction efficiency by pulsed ultrasound at 152 kHz has been studied experimentally through absorbance measurements of triiodide ions from sonochemical oxidation of potassium iodide at different liquid volumes to determine sonochemical efficiency defined by reacted molecules per input ultrasonic energy. The mechanism for enhancement of the reaction efficiency by pulsed ultrasound is discussed using captured images of sonochemiluminescence (SCL), and measured time-resolved signals of the SCL pulses and pressure amplitudes. The high. sonochemical-reaction efficiency by pulsed ultrasound, compared with that by continuous-wave ultra-sound, is attributed both to the residual pressure amplitude during the pulse-off time and to the spatial enlargement of active reaction sites.