The chemical reduction of hexavalent chromium (Cr(VI)) by combined zerovalent magnesium (ZVMg) and ultrasound (US) was studied under batch conditions. Results have demonstrated that the reduction of Cr(VI) mediated by ZVMg enhanced significantly with the ultrasonic effect. The percent reduction of Cr(VI) by ZVMg (5 g/L) was about 20 % after 60 min, but its complete reduction was attained within an hour when ultrasound was applied at a power of 100 W. The efficiency of Cr(VI) reduction increased with increasing ultrasonic power and magnesium dose. The synergy of the combined treatment has been attributed to the surface activation of ultrasonic treatment. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), atomic absorption spectrophotometer (AAS), pH, and X-ray diffraction (XRD) analyses have revealed that magnesium and chromium hydroxides and hydroxide ion were three major by-products during the reduction of Cr(VI) by US/ZVMg under pH-uncontrolled conditions. The proposed method does not require acid and buffer addition and has an advantage of removing Cr(VI) and its by-product (Cr(III)) simultaneously.