Various cresyldichlorothiophosphates have been synthesized and applied as flame-retardant formulations on cellulose. Thiophosphorylated cellulose samples have been investigated by DTA and TG techniques from ambient temperature to 600 degrees C in a static aii atmosphere. On the DTA trace of each sample, three or four peaks were observed. The first peak was endothermic and the others were exothermic. The first exotherm was caused by the decomposition process and was lower than that of pure cellulose. The Broido method was used to obtain various kinetic and thermodynamic parameters from the TG curves. The values of the activation energy for the decomposition stage of thiophosphorylated cellulose samples were in the range of 78 to 120 kJ mol(-1) and are lower than that of pure cellulose (193 kJ mol(-1)). The EPR signals indicated the formation of very few free radicals during the thermal degradation of these samples. Char yields of these samples, at decomposition temperatures, indicated that the formation of char is brought about at the expense of decrease in the decomposition temperature of the relevant exothermic peak. Further, higher char yields of different cellulose cresylthiophosphate samples, compared to cellulose phenylthiophosphate and cellulose itself, lead to the conclusion that cellulose cresylthiophosphates are good flame retardants.