Characteristics of heat transfer were investigated in pressurized slurry bubble column reactors whose diameter was either 0.051, 0.076, 0.102 or 0.152 m (ID) and 1.5 m in height, respectively. Effects of gas velocity (U(G)), solid contents (S(C)), pressure (P), liquid viscosity (μ(L)) and column diameter (D) on the heat transfer coefficient (h) between the immersed vertical heater and the column were determined. Multiple effects such as U(G) and D, P and D, μ(L) and D, and S(C) and D on the value of heat transfer coefficient were discussed. Temperature fluctuations were also measured and analyzed by adapting chaos theory, which was used to explain the effects of operating variables on the heat transfer in the column. The heat transfer coefficient increased with increasing gas velocity, pressure or solid content in the slurry phase, but decreased with increasing liquid viscosity or column diameter. The decrease trend of h with increasing column diameter was somewhat sensitive when the gas velocity was relatively high (U(G)≥12 cm/s). The effects of column diameter on the h value became almost linear when the operating pressure (P=4-10 kgf /cm2), liquid viscosity (μ(L)=20-38 mPa·s) or solid content in the slurry phase (S(C)=10-20 wt%) was relatively high and gas velocity was relatively low, within these experimental conditions. The heat transfer coefficient was well correlated in terms of dimensionless groups as well as operating variables.