Both the generation of a microporous structure and char formation kinetics have been studied in the pyrolysis of sawdust of Pinus insignis in a conical spouted bed reactor, in the range 350-700 degrees C. The BET surface area (representative of the physical evolution of the solid) and the C/H ratio of the solid (representative of the chemical structural change) have been taken as conversion indices. From the measurement of the C/H ratio of the solid (the more significant variable), it has been determined that the reaction order is 0.5 and that the kinetic constant is between 0.18 min(-1) at 350 degrees C and 1.26 min(-1) at 700 degrees C. However the value of the constant is almost independent of temperature, at 1 min(-1) in the range 500-700 degrees C.