A particle image scope consisting of an image fiber and a video system was developed to perform microscope observations of solid particles in circulating fluidized beds (diameters of risers : 60 mm and 100 mm; height : 4500 mm and 5500 mm, respectively). The behavior was examined using coarse sand particles (d(p) = 0.30 mm, U(mf) = 0.10 m s-1) and fine sand particles (d(p) = 0.057 mm, U(mf) = 0.002 m s-1). The images obtained clearly showed the shape and the number of the solid particles. The particle velocity was also determined by adjusting the exposure time of the 35 mm camera or video camera. Therefore, the variation of the solid holdup as a function of time, or the particle velocity, was easily obtained. ne results show that the particle image scope developed here is quite effective in the microscope observation of gas-solid flow.