Temperature fluctuations and heat transfer characteristics were investigated in a fluidized-bed combustor of 0.102 m ID and 2.5 m in height, which was designed for waste oil combustion. Effects of excess air (A_E), injection height (H_I) and feeding rate of waste oil (Q_F) on the mean bed temperature (T_B, Kolmogorov entropy (K₂) of phase space portraits and heat transfer coefficient (U_O) in the fluidized-bed combustor were determined. T_B increased, but K₂ and U_O decreased with increasing A_E. K₂ had a local minimum, but T_B and U_O had a maximum at H_I of 0.4 m. T_B increased, but K₂ had a minimum and U_O had a maximum with increasing Q_F in the combustor. T_B, K₂ and U_O obtained at the optimum operating condition (A_E=40%, H_I=0.4 m, Q_F=30 g/min) were about 855 ℃, 22 bits/s and 382 W/m²K, respectively.