Abstract. Mahdiyanti SH, Tsuchikawa S, Mitsui K, Tolvaj L. 2020. Steaming-caused chemical changes of sugi (Cryptomeria japonica) wood monitored by NIR spectroscopy. Asian J For 4: 7-10. Sugi (Cryptomeria japonica D. Don) wood samples were steamed, applying a broad range of steaming time (0-20 days) at 90 and 110°C steaming temperatures. NIR spectroscopy was used to monitor the chemical changes caused by steaming. The difference spectrum method was applied to find the absorption increases and decreases. Before the subtraction, the spectra were normalized to one unit at 1739 nm to eliminate the parallel shift of the spectra. Steam-induced chemical changes in the wavelength range of 1300-2100 nm are related to the absorption of water and the absorption of extractives, especially phenolic contents. These chemical changes are suspected to be strongly related to color changes in steamed wood. Longer duration of steaming caused phenolic compounds to change into similar contents in all wood tissues, which cause their color to change more uniformly. Steaming caused a water bounding capacity loss of the cell wall. This change was much faster at 110°C than at 90°C.