The effects that the gasification temperature (550~850℃) and partial pressure of H₂O (25~101.3 kPa) have on the steam gasification rates of tire-char and sludge-char have been determined in a thermobalance reactor. The gasification rates followed the order: tire ＞ coal ＞ sludge. Among the tested gas-solid reaction models, the modified volumetric reaction model was most appropriate to predict our conversion data and, thus, the kinetic parameters were determined on the basis of a modified volumetric reaction model. From the Arrhenius plot (κ - vs. 1/T), the activation energy and the pre-exponential factor were 39.1 kJ/mol and 0.2669 s^(-1), respectively, for tire-char and 156.5 kJ/mol and 5.8611×10⁴s^(-1), respectively, for sludge-char. The reaction orders were 0.87 for tire-char and 0.96 for sludge-char, with respect to H₂O partial pressures of 0.25~101.3 kPa. The gasification reaction rate can be expressed as dX/dt=(0.2699)exp(-39090/RT)(P_(H₂O))^(0.87)(1-X) for tire-char and dX/dt=(58611)exp(-156510/RT)(P_(H₂O))^(0.96)(1-X) for sludge-char.