Teak (Tectona grandis) has been popularly known in the wood industry as a precious material due to its natural dimensional stability. To explore the main components affecting the dimensional stability of teak wood, the teak wood samples were extracted with different polar solvents, and the extractives were impregnated into rubberwood specimens to determine their effect on the dimensional stability of the modified rubberwood. The results showed that the methanol extractives of the teak wood exhibited the most significant effect on the dimensional stability of the rubberwood. The extractives were characterized by infrared (IR) and gas chromatograph/ mass spectrum (GC/MS). The GC/MS results showed that the methanol extractives primarily contained 9,10-anthracenedione, 1,1-dimethyl-3,4-bis(1-methylethenyl), and alcohol compounds. It was speculated that the alcohol compounds in the methanol extractives reacted with polar hydroxyl groups in the cell wall, which resulted in a decrease in the size of the site combined with bound water. Moreover, the hydrophobic hydrocarbon compound was impregnated into rubberwood to form a thin layer of protective film in the cells into which the water could not enter under 20 °C and 80% RH.