Abstract: To better understand the torsional mechanism and influencing factors of a PC composite box-girder with corrugated steel webs,the ultimate torsional strength of four scaled specimens under pure torsion was studied.Monotonic pure torsion acts on specimens by eccentric concentrated loading.The experimental results show that cracks form at an angle of 45° to the member’s longitudinal axis at the top and bottom of concrete slabs.Longitudinal reinforced steel bars located at the center of cross section contribute little to the torsional capacity of the specimens.The torsional stiffness is proportional to the corrugation parameter ηand there is an increase in yielding torque of steel webs and the ultimate torque of specimens increase as the thickness of corrugated steel webs.