Heat transfer characteristics have been investigated in the riser of gas-liquid circulation and three-phase circulating fluidized-bed bioreactors whose diameter and height are 0.102 m and 1.0 m, respectively. Effects of gas and liquid velocities and holdup of fluidized biofilm media on the heat transfer coefficient between the immersed vertical heater and the bed have been determined. The heat transfer coefficient in the gas-liquid circulation reactor increases with increasing gas velocity, but increases only slightly with increasing liquid velocity. The h(heat transfer coefficient) value in the three-phase circulating fluidized-bed bioreactor also increases with increasing gas velocity or holdup of fluidized biofilm media, but it increases only slightly with liquid velocity. The value of heat transfer coefficient has been well correlated in terms of operating variables.