Benzothiophene (BT) decomposed rapidly following pseudo-first-order kinetics by ultrasonic irradiation in aqueous solution. The rate constant increased with increasing ultrasonic energy intensity. Hydroxybenzothiophenes, dihydroxy-benzothiophenes, and benzothiophene-dione were identified as reaction intermediates. It was proposed that benzothiophene was oxidized by OH radical to sequentially form hydroxybenzothiophenes, dihydroxybenzothiophenes, and benzothiophene-dione. Evolution of carbon dioxide and sulfite was also observed during ultrasonic reaction. Kinetic analysis suggested that approximately 77% of the benzothiophene decomposition occurred via OH radical addition. Pathways and a kinetic model for ultrasonic decomposition of benzothiophene in aqueous solution were proposed.