In this study, as the flame-retardant finishing process, a mordant-dyeing process was used. The flash point and ignition point for Cr-mordant and Ti-mordant dyed worsted yarns were measured. The results of this process and the analysis of DTA and TGA are summed up as follows: 1. The flame-retarding effect of Ti mordanting with the metal salt is better than that of Cr-mordanting with metal salt. 2. In the analysis of TGA, initial weight loss of Cr- or Ti-mordanted dyed worsted yarn is greater than that of unfinished yarn. 3. The effect of flame retarding is better when the initial pyrolysis lasts longer at low temperature.