From a commercial viewpoint, the two most promising methods of producing biodegradable polymer materials are: (i) to blend poly(lactic acid) (PLA) with starch and (ii) to reinforce it with cellulose fibres, since both additives are commercially available and are derived from renewable resources. This paper reports on a study of the effects of starch and wood flour (WF) on the thermal stability of PLA using thermogravimetric analysis (TGA) in a nitrogen atmosphere, and TG-FTIR to investigate the effects of degraded products from the two fillers on the thermal degradation of PLA. Both fillers accelerated decomposition by releasing chemicals, in particular those with polar groups that can act as chain scissors in PLA. The lower decomposition temperature of the starch resulted in lower decomposition temperatures for PLA/starch blends compared to PLA/WF composites. In addition, the smaller particle size of the starch compared to the WF, facilitated greater interfacial contact with the PLA matrix, thus enhancing its function in accelerating decomposition. (C) 2010 Elsevier B.V. All rights reserved.