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 (AE), injection height (HI) and feeding rate of waste oil (QF) on the mean bed temperature (TB, Kolmogorov entropy (K2) of phase space portraits and heat transfer coefficient (UO) in the fluidized-bed combustor were determined. TB increased, but K2 and UO decreased with increasing AE. K2 had a local minimum, but TB and UO had a maximum at HI of 0.4 m. TB increased, but K2 had a minimum and UO had a maximum with increasing QF in the combustor. TB, K2 and UO obtained at the optimum operating condition (AE=40%, HI=0.4 m, QF=30 g/min) were about 855 ℃, 22 bits/s and 382 W/m2K, respectively.