This paper presents a new methodology to measure sediment concentration using the Contact Image Sensor in the boundary layer. The detectable range of the sediment concentration was found to be sensitive to the sediment particle size (d 50 ). It is found that in the siliceous sand mixture the CIS best works at the concentration range from 0.1∼50 kg/m 3 . The narrow sediment-laden layer induced by unidirectional steady current (with C > 10 kg/m 3 and average layer thickness ranging 3 mm∼17 mm) in the close vicinity of a sand bed was detected with the sensor at different flow intensities. And the stratification in the sediment concentration was observed to be in reasonable agreement with existing empirical predictions in the literature.