A system for controlling a thickness of a strip being rolled by a rolling mill having more than two rolling stands, in tandem configuration. A subcontrol unit controls a rolling speed and a rolling load of a final rolling stand according to a predetermined control schedule. A plurality of tension gauge units installed between adjacent rolling stands detect a tension of the strip. A plurality of thickness gauge units including at least first thickness gauge unit installed on the output side of a first rolling stand, second thickness gauge unit installed on the output side of a penultimate rolling stand, and final thickness gauge unit installed on the output side of the final rolling stand, detect a deviation in the thickness of the strip from a predetermined value. A thickness control unit, connected to the tension gauge units and the thickness gauge units, controls the thickness and the tension of the strip to respective predetermined values by adjusting a roll gap and the rolling speed of the rolling stands except the final rolling stand, based on the detected tensions and the detected deviations of the strip. A feedback unit controls a rolling speed of an antepenultimate rolling stand according to the detected deviation of the last thickness gauge unit and the detected deviation of the second thickness gauge unit to adjust the thickness of the strip to the predetermined value.