The effect of kaolin loading on the viscosity and shear strength of natural-rubber-based pressure-sensitive adhesive was studied using coumarone-indene resin, toluene, and polyethylene terephthalate as tackifier, solvent, and substrate, respectively. Kaolin loading ranged from 10 to 60 parts per hundred parts of rubber (phr) whereas the tackifier content was fixed at 40phr. The viscosity and shear strength-from lap shear test-were determined by a Brookfield viscometer and Lloyd adhesion tester, respectively. Results show that viscosity increases with increasing kaolin loading. However, shear strength increases up to 20phr kaolin loading, after which it decreases with further filler loading. This observation is attributed to the culmination of cohesive strength at the optimum loading of kaolin filler. For a fixed kaolin loading, the shear strength increases with coating thickness and testing rate.