The effects of three retardants, NH4Cl, (NH4)(2)SO4 and NH4H2PO4, on the thermal decomposition of wood-derived rayon fiber have been investigated by thermogravimetry-mass spectrometry (TG-MS) analysis. The main thermal decomposition of pure wood-derived rayon fiber, like other cellulosic materials, takes place rapidly over a narrow temperature range. When wood-derived rayon fiber is impregnated with the fire retardants, there is a shift in the temperature of maximum rate of weight loss to the values lower than 300 degreesC, while the amount of char residue formed is increased. The fire retardants have resulted in the increase of the intensity (peak area) of m/z = 18 and 28 MS signals, but the decrease of the intensity of m/z = 44 MS signals. Furthermore, it appears with a relative decrease of the intensity of m/z = 60 and 68 MS signals, which means that low levels of levoglucosan and levoglucosenone are recorded in the presence of the fire retardants. Finally, the relationship between char residue formation and the relative quantity of levoglucosan is determined. (C) 2004 Elsevier B.V. All rights reserved.