An on-line system for measuring the thickness variations in jute sliver coming out of a carding machine has been described. The system uses an ultrasonic transmitter-receiver matched pair for sensing the vertical displacement of delivery roller through which the jute sliver is passing. This, when calibrated, gives a measure of the thickness variation in sliver. Since the sensing is of non-contact type, the transducer maintenance is minimum. The details of electronic circuitry and test results are given.