It has been shown that the thermal treatment (<100 ° C) of cellulose fibers for periods shorter than 24 hours causes, additionally to the yellowing, the increment in tensile strength, elasticity modulus, toughness and resiliency, besides less plastic deformation in fibers after traction. These phenomena were interpreted from changes in hydrogen bonding monitored by FTIR. Aiming at evaluating changes in the mechanical strength of bleached eucalyptus fibers, samples were subjected to thermal treatment at temperatures ranging from 60°C to 100°C. The optical and mechanical properties, structure of linkages and crystallinity were monitored. Each year, new applications are developed by inserting the pulp as fibrous or not raw material, in increasingly diversified segments. The increase in the strength of the samples after thermal treatment has been justified by the increased interfiber interaction and possibility of formation of interplanar hydrogen bonding. The thermal treatment, in the settings used here, representing a good alternative for predicting the behavior of cellulose pulp optical properties.