A study was performed to elucidate the influence of biomass type on char steam gasification kinetics. Isothermal experiments were carried out in a thermobalance in chemical regime on nineteen biomass chars produced under the same conditions. The reactivity obtained varied of a factor of more than thirty. This large difference appeared to be correlated with the biomass inorganic elements. In particular, the catalytic effect of potassium (K) as well as the inhibiting effect of silicon (Si) and phosphorus (P) were highlighted. Three different types of rate evolution versus conversion could be observed depending on the ratio K/(Si + P) and were correlated with the ash surface composition after gasification. Conversion could be satisfactorily predicted versus time through simple models taking into account the influence of inorganic elements and thus further useable in simulation of industrial gasifiers fed by various biomass types.