Kaolin was modified with a solution of phosphorylated cashew nut shell liquid prepolymer (PCNSL) containing hexamethylenediamine (HMDA). The organomodified kaolin was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and infrared spectroscopy (FTIR). Processability characteristics and physico-mechanical properties of natural rubber (NR) compositions of conventional vulcanization (CV), semi efficient vulcanization (SEV) and efficient vulcanization (EV) systems containing 6phr (parts per hundred rubber) of the HMDA-PCNSL modified kaolin and unmodified kaolin have been studied. Compositions containing the organomodified kaolin showed improved cure characteristics and vulcanizate properties such as hardness, tensile strength, tear strength, abrasion resistance and thermal stability along with lower heat build-up and compression set which could be advantageous for applications such as tire treads.