The oxidation reactions of cellulose involve the primary and secondary hydroxyl groups of the pyranose ring and result in carbonyl and carboxyl groups. This reaction can be accompanied by opening the pyranose ring. In any cases the glucosidic bond becomes weaker; the formation of carboxyl groups induces a depolymerisation, thus reducing the polymerisation degree and the physical and mechanical strength of the material. The conversion of 1,2-dihydroxyl groups to dialdehyde by periodate oxidation on cellulose based materials as textiles (flax and cotton) and paper with different composition and characteristics, has been studied. To investigate the cellulose behaviour at different level of oxidation, two different solutions of sodium methaperiodate were used: 0.1 and 0.4 M, for different times of treatment. The oxidised samples become "models" to investigate the different levels of degradation in real materials. Thermal analysis is convenient and reproducible, and is a useful method for characterising heterogeneous organic materials from plants. In this research we have examined the assignment of the exothermic transition in DSC analysis of paper, flax and cotton and its components in order to understand their thermal behaviour in more detail and to evaluate the effect of the oxidation treatment on the thermal behaviour. The aim of our work is to correlate the level of degradation of the oxidised samples with the natural ageing of the real cellulose based materials. The results obtained suggest information in the restoration and conservation field of cellulosic materials. (C) 2004 Elsevier B.V. All rights reserved.