Eucalyptus grandis x Eucalyptus urophylla `GLGU9' is one of the most commonly planted tree species in South China. It is a new variety created a fast-growing species, the poor dimensional stability is one of its main drawbacks, which restricts its applications. Thermal treatment is one of the effective methods to improve the dimensional stability of wood. GLGU9 wood was treated using thermal modification with palm oil. The oil was used as a heating medium and a shielding material at temperatures of 150, 170, 190, 200, and 210 degrees C, at various treatment durations of 1.5, 3, 4.5 and 6 h. To investigate the effect of palm oil thermal treatment on dimensional stability, the anti-shrink efficiency (ASE,) and anti-swelling efficiency (ASE2) were examined. The results indicated that the ASE, and ASE2 were increased by 62.8% and 56.6% at 210 degrees C for 6 h treatment, respectively.