Solid fraction distribution in a cyrindrical jetting fluidized bed with a center nozzle was measured with an optical fiber probe. The effects of air flow rate through the nozzle, shape of distributor and background air through the distributor on various phenomena were investigated. When a cone shaped distributor was used, jet height, defined as the height from where the solid fraction of the center became a certain value, increased with increasing air flow rate through the nozzle, and its value was close to that estimated by Yang and Keairns＇ correlation (1979). When a flat distributor was employed, the solid fraction in the jet was higher and the diameter of the jet was larger, but jet height was lower than that when the cone shaped distributor was employed. In the case without background air, a high concentration region was observed in the annulus. and both the jet height and jet diameter became larger, but solid fraction became lower in the jet.