A new approach to improve the thermal stability [GRAPHIC] and mechanical strength of thermoplastic polyester elastomer (TPEE) using spodumene slag as the filler is reported here. The thermal decomposition temperature of TPEE increases from 277 degrees C to about 350 degrees C by about 26% in the presence of pristine spodumene slag. The surface graft reaction further improves its barrier effect. Besides, spodumene slag can be used as a good reinforcement to TPEE, and also the surface treatment favors further improvement of its reinforcing effect. However, the presence of spodumene slag reduces the elastoplasticity and viscoplasticity of the system, leading to decreased tensile cycles and elongation levels. The morphological and crystallographic methods were then employed to further reveal the alteration of the phase separation structure of TPEE in the presence of spodumene slag, aiming at establishing structure-property relations of composites. This work can provide useful information on the preparation of new TPEE composites with tailorable properties.