Two sets of thermogravimetric curves of isothermal degradation of beech wood have been measured for temperatures between 528-584 and 573-708 K, respectively. The reduced sample size (layers 150 μm thick) and the moderate temperatures establish a kinetically controlled process. The curves are well described by a global degradation mechanism consisting of three sequential steps. The kinetic constants estimated for the first-order reaction rates are: (I) ln A 1 =10.2+/-4.5 s.1 and E 1 =76.2 kJ+/-21.1 mol - 1 ; (II) ln A 2 =22.5+/-2 s - 1 and E 2 =142.8+/-10 kJ mol - 1 ; and (III) ln A 3 =2.3+/-1 s - 1 and E 3 =43.8+/-5.7 kJ mol - 1 . Good agreement is obtained with previous dynamic (I and II step) and isothermal (II step) analyses.