The degradation kinetics of untreated and rain-leached (wheat) straw have been investigated under isothermal conditions (500-650 K) in a weakly oxidative atmosphere. For both cases, weight loss curves follow a two reaction zone mechanism. In the first, fast volatile release results in about 20-70% solid conversion, followed by further slow solid devolatilization. A semiglobal kinetic mechanism is proposed and the kinetic constants are estimated for the two reaction zones and the formation of the volatile and the solid-phase product classes. For both cases, the activation energy of the first zone is higher than that of the second, but leaching significantly reduces the reaction rates at low temperatures for the first zone and high temperatures for the second zone.