The gasification of biomass is a thermal treatment which results in a high production of gaseous products and small quantities of char and ash. In the literature a large number of experimental studies concerning the gasification of biomass with air and oxygen has been presented; generally, in these processes the heat for the gasification is produced in the reactor with a partial oxidation of biomass. However, only a few data are available for the gasification with indirect heating that produces a gas richer in energy. The aim of this paper was to study the influence of the operating conditions on the gasification of biomass carried out in a pilot plant. The process consisted of a steam gasification carried out in two indirectly heated reactors in series. Some experimental results concerning thermal and catalytic runs are presented.