The effects of surface modification of ground calcium carbonate (GCC) particles on the thermal and mechanical properties of poly(vinyl chloride) (PVC) based composites were investigated. Aminopropyltrimethoxysilane (APS) was used as a modifier for GCC particles. The experimental results indicated that the pre-treatment of GCC particles with NaOH promoted the formation of OH- on the surface of GCC particles, which improved the graft of APS on GCC surface and enhanced the interfacial interaction between GCC particles and PVC matrix. The SEM micrographs of the PVC filled with different GCC particles showed that the dispersion of fillers in the PVC matrix was improved by surface modification. The results of TG showed that the thermal properties of PVC filled with NaOH/APS modified GCC particles (PVC/GCC-OH-APS) outweighed those of PVC filled with APS modified GCC particles (PVC/GCC-APS) or raw GCC particles (PVC/GCC). Compared with the use of raw GCC, the use of the surface modified GCC particles, especially the GCC-OH-APS, led to the increase of the tensile strength and impact strength of the composites.