To provide a treating agent for seat belt webbing excellent in smoothness and abrasion resistance at room temperature and low temperature, and a method for treating the same.

The treating agent for seat belt webbing includes a polyether polyester compound (A) expressed by the following general formula (1), liquid in appearance at -20C, and having a number average molecular weight of 2,000-15,000, as an essential component. In the formula (1): R1-(Q-X)n-Q-R2 (1), G represents a divalent carboxylic acid residue; X represents the residue of a polyether diol compound (a); R1 and R2 each independently represent H, a monovalent alcohol residue, or the residue of an alkylene oxide (2-4C alkylene oxide) of a monovalent alcohol, however, both R1 and R2 do not (simultaneously) represent H; n is a number of 1-20.