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The objective of this work was to verify the dimensional behavior of heartwood wood and sapwood submitted to different temperatures. It was evaluated volumetric, sectional and linear dimension reduction in heartwood and sapwood of Hymeneae courbaril L submitted to final temperatures of 200º, 300º, 400º, 500º, 600º, 700º, 800º and 900°C, in an electric kiln with medium rate of heating of 1.3ºC/minute. For the measurement of the dimensions, accomplished before and after the thermal treatments, an image analyzer (Midro-Videomat Zeiss) was used. It was obtained, with base in the individual readings accomplished in the image analyzer, the rates of longitudinal and traverse linear, longitudinal and traverse sectional and volumetric reduction. The results showed that tem- perature increase of 1000C, average reduction rate reached 2.55% and 4.24%, 5.95% and 7.21% and 8.36% in the longitudinal and traverse linear dimensions, longitudinal and traverse sectional and volumetric, respectively, for heartwood. For sapwood the values were, respectively, 2.64% and 5.02%, 6.70% and 8.17% and 9.15%. For both sapwood and heartwood the largest reduction rates occurred in temperatures between 300º and 5000C. The heartwood presented larger resistance to the action of the temperature, however its thermal decomposition was more pronounced than that of sapwood in the temperature range of 200-300 0C. This behavior is similar to that of lignin in relation to cellulose.