Heat treatment of Grevillea robusta, a tropical wood species of low natural durability, was carried-out under inert conditions to improve its decay resistance. Resistance of heat treated samples was evaluated by malt agar block tests after three months of exposure to several wood rotting fungi. Also resistance of heat treated wood against termites was tested in the laboratory and in the field. Results showed that durability against fungi and termites was greatly improved after treatment. There was a good correlation between decay resistance and mass loss due to thermal treatment. Microscopic, FTIR and (13)C MAS NMR analysis were performed to characterize wood chemical and anatomical modifications that occur after treatment to understand the reasons of the durability improvement.