Pyrolyses of rice hulls were performed in a thermogravimetric analyzer from room temperature to 1173 K at heating rates of 10, 30, 60, and 100 K/min. The global mass loss during rice hull pyrolysis was modeled by a combination of the volatile evolutions of four independent parallel lumps : one for moisture and the other three for nonmoisture volatiles. The decomposition of each lump was characterized by a single reaction, first-order with respect to the amount of volatile yet to evolve. The moisture lump evolves mainly at low temperatures with an activation energy of 48 kJ/mol. The activation energies for the evolution of the nonmoisture volatile lumps, which are attributed to the decompositions of hemicellulose, cellulose, and lignin, are 154, 200, and 33 kJ/mol, respectively. Excellent agreement between the experimental data and model predictions was found.