The effect of zinc borate (ZnB) was studied on the flame retardant and thermal properties of thermoplastic polyurethane containing huntite-hydromagnesite. The flame retardant properties of thermoplastic polyurethane-based composites were investigated using limiting oxygen index, vertical burning test (UL 94), thermogravimetric analysis, and mass loss calorimeter. No remarkable effect of ZnB was observed on the flammability properties of composites. UL 94 rating did not change regardless of the added amount of ZnB, and the slight increase in limiting oxygen index value was observed at ratio of 1:1. The adjuvant effect of ZnB was observed during the mass loss calorimeter studies by increasing the barrier effect of the residue in the condensed phase and by increasing the formation of incombustible gasses in the gas phase. The highest fire performance was achieved at ratio of 1:1.