The present studies are focused on the effect of different polymer solutions, e.g. chitosan and polyvinyl alcohol (PVA) on the mechanical properties of the paper sheets. The improvement in the mechanical properties of the treated paper sheets with chitosan is higher than that in the other polymer solution. Moreover, the heat resistance of treated paper sheet with chitosan is more improved than with other polymer. The activation energy of the thermal treatment of untreated and treated paper sheets with mixed polymers solution is also calculated. (C) 2004 Elsevier B.V. All rights reserved.