Abstract: Good formulations of drilling fluid properties are required in drilling operations. Selection of suitable drilling fluid additives are important criterion in formulating drilling fluid. Nanomaterial is selected in this study due to its extremely high surface area to volume ratio and high thermal conductivity. This research is focused on determining the optimum concentration of multi-walled carbon nanotubes (MWCNTs) to produce better rheological properties in water-based and ester-based drilling fluids at various temperatures. Different concentrations of MWCNTs at various temperature were tested in this study. The results revealed that in water-based drilling fluid, the plastic viscosity, yield point and gel strength are not much affected by different concentration of MWCNTs used. However, 0.01 ppb of MWCNTs gives the lowest filtrate volume at low pressure low temperature and high temperature high pressure condition of 4.4 and 1.9 mL, respectively. In ester-based drilling fluid, gel strength and emulsion stability is slightly increased as MWCNTs concentration increases. This formulation also indicates that MWCNTs can be used together with conventional filtrate loss control agents to improve filtrate loss. It is also found that temperature gives an effect to the drilling fluid rheological properties. In water-based drilling fluid, plastic viscosity, yield point and gel strength are decrease with an increase in temperature. On the contrary, ester-based drilling fluid shows the other way around. Therefore, MWCNTs can be used as an additive in drilling fluid due to its improvement observed in the drilling fluid rheological properties.