High-intensity ultrasound, is sought as a means to break particles. A horn-type ultrasonic transducer is used to apply HIU into a suspension of alumina particles causing breakage to occur. The rate of particle breakage is monitored continuously via in-line laser-based particle chord length measurement. Kapur function analysis is used to arrive at the grinding kinetics under variations of ultrasonic power, particle loading, temperature of the suspension and particle size. The first Kapur function increases monotonically with increase in input ultrasonic power. Increasing temperature also increases the first Kapur function but an optimum in the range investigated (10-50 degrees C) is observed near 25 degrees C. An exponential relation is found for the variation of first Kapur function with particle size, this being unique to ultrasound-mediated particle breakage. The breakage mechanism is attributed mainly to particle abrasion. Different breakage mechanisms are observed at different temperatures. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 2025-2035, 2011