To obtain the subject composition long in a pot life, bondable in a short time, useful as a flexible printed circuit board, capable of providing sufficient flame retardance, by blending a thermoplastic polyester resin with an isocyanate, a specific flame-retardant and a flame-retardant auxiliary in a prescribed ratio.

This flame-retardant adhesive composition is obtained by blending (A) 100 pts.wt. of a thermoplastic polyester resin [e.g. two kinds of resins having different glass transition temperatures (Tg), especially a mixture of a resin having 50 to 80°C Tg and a resin having -30 to 20°C Tg in the blending ratio of 2:8 to 8:2, (B) 2-10 pts.wt. of an isocyanate such as tolylene diisocyanate, (C) 30-60 pts.wt. of a halogen-based flame-retardant such as decabromodiphenyl ether and (D) 20-60 pts.wt. of antimony trioxide.