Mean heat transfer coefficient h(s) around a single, horizontal pipe settled in a fast circulating fluidized bed was measured under various fluidizing condition. The heat transfer coefficient could be correlated well with the solid fraction in gas-solid mixture flow, being a function of solid circulating rate, gas velocity and riser position. The value of h(s) increased as the solid circulating rate became high. However, it was found that there was a critical solid fraction, ranged from 0.01 to 0.02, over which the increasing ratio dropped to a smaller one. This phenomenon was considered to be due to a characteristic change of the particle behavior around pipe.