Three heat-treatment schedules were applied to $90{ imes}90mm$ dimension square lumber of Pinus koraiensis, one of major domestic species, and their colors and physical properties were investigated for obtaining an optimum schedule. Each square lumber was heat-treated three times. The temperatures of $170^{circ}C$ and $190^{circ}C$, and the time of 9 hours and 13 hours were used for the first heat-treatment. The schedule of $190^{circ}C$ and 7 hours were used for the next two heat-treatments. The averages of brightness $L^*$ decreased linearly as the heat-treatment repeated and its standard deviations also decreased slightly. While the averages of color difference ${Delta}E^*$ increased linearly as the heat-treatment repeated and its standard deviations also increased slightly. The average compressive strength of the heat-treated specimen was higher than that of the control by 9%, which deviates from previous reports. ASE and WPG of the heat-treated specimens were measured to confirm that heat-treatment improved dimensional stability significantly.