Com. starch was compounded with cellulose fibers (up to 30% by mass), plasticized with glycerol (20% by mass), granulated by extrusion at 80-120 degrees C and screw speed 60-100 rpm, and finally studied for thermal decompn. by thermogravimetry in air (up to 1173 K). Three-stage decomposition was obsd. During the 1st stage (up to 473 K), only weak chem. bonds were destroyed. During the 2nd stage (up to 673K), the composite material was oxidized mainly to CO2. During the 3rd stage, combustion of C took place. Decompn. rate consts., reaction orders, activation energies and pre-exponential factors were calcd. from the exptl. data. The addn. of fibers resulted in a decrease in thermal resistance of the composite material.