In this study, a newly developed image calibration method is compared with an optical fibre probe in the measurement of the solids holdup of FCC particles in a 7.6m narrow rectangular circulating fluidized bed (CFB) riser. The image calibration method is based on experimentally correlating solids holdup of FCC particles in the CFB and the grayscale of the corresponding images obtained by a high speed video camera. Using this method, solids holdups along 15 lateral positions are calculated under different operating conditions with U-g and G(s) in the range of 3.0-12.0m/s and 50-150kg/m(2)s. The solids holdup lateral distribution profiles obtained from the two methods in this study under identical operating conditions coincide with each other fairly well, reflecting the reliability of the image calibration method. Further comparison of the results of image calibration method from the current study with the measurement results of optical fibre probe from other researchers also show good agreement under the same operating condition. These comparisons clearly confirm the feasibility and accuracy of the image calibration method.