Direct detection of didecyldimethylammonium chloride (DDAC) and cyproconazole in western hemlock (Tsuga heterophylla) square lumbers impregnated with quaternary ammonium or copper azole preservatives was conducted by using pyrolysis-gas chromatography/mass spectrometry. These components could be detected from 200-300 μg of milled wood samples prepared from the each treated lumber without interference of major components and extractives of wood. It was shown that quantitative detections of DDAC and cyproconazole were possible from the concentration of 0.1% W/W and of 0.04% W/W, respectively.