Abstract: The residual Cr in tannery sludge cannot be recovered efficiently by traditional acid leaching. To resolve the problem, a process scheme of ultrasonic assisted acid leaching was proposed to realize the harmlessness of tannery sludge and the efficient recovery of Cr . The results indicated that the removal of Cr by acid leaching increased with the duration of ultrasonic treatment. Total organic carbon (TOC) raised from 937.5 mg/L to 1571.4 mg/L under the condition of 0.5 mol/L H₂SO₄, ultrasonic power of 50% (1800 W) and leaching time of 40 min, while VSS declined from 49.9% to 10%, leaching efficiency of Cr reached 90.61%, and the residual Cr could be reduced to less than 4.4 mg/g. The results verified that ultrasonication obviously intensified the efficiency of acids extraction of Cr from sludge with significant synergic effect. The ultrasonic assisted acid leaching process provides an efficient and feasible solution for the breakdown of complex structure and the release of residual Cr in the tannery sludge.