The potential of utilising corncob and sugar cane waste as viscosifier for hydrocarbon drilling fluid was investigated. A synthetic-based drilling fluid, Sarapar 147, was used as the base fluid. Both materials were subjected to pre-treatment procesess: drying, dehumidifying, grinding and sieving, prior to rheological tests. Rheological tests were conducted in accordance to API 13B specifications to measure mud density, plastic viscosity, yield point, 10-second and 10-minute gel strengths. The study found that the plastic viscosity and yield point had a direct relationship with the amount of materials added. For the drilling fluid additive with corncob and sugar cane waste, it was found that as the amount of additives increased, the density, plastic viscosity and yield point increased as well. Based on experiments, both additives showed potential to be used as a viscosifier in hydrocarbon drilling fluids, i.e. better rheological properties by increasing density, plastic viscosity and yield point. The suitable dosage for corncob and sugar cane waste is 6.45 lb/bbl and 9.43 lb/bbl respectively.