Oil based mud (OBM) is well known in drilling operation for its good properties. However, under HPHT conditions, OBM might encounter thermal degradation, which will affect the performance of the mud leading to fluid loss and unstable rheology. Previous studies showed that implementation of nanoparticle as drilling mud additive can control the fluid loss into the formation thus preventing formation damage. In this research we evaluate the potential of using nanoparticle from silica as the fluid loss preventing agent. The OBM was used in this study and its performance at low and high temperature was evaluated after addition of nanosilica powder. The experiment was conducted at 275°F and 350°F with varying nanosilica concentration per amount of a commercial fluid loss control additive (gilsonite) between 30 to 70 , by total mud weight between 0 to 2 wt. . Result of the study shows that the application of nanosilica in OBM results in better mud rheology and can effectively reduce fluid loss up to 50 concentration especially at HPHT conditions. The silica nanoparticles have the potential to enhance drilling fluid properties, which contributes to more efficient drilling operations with less formation damage. This finding would be economically beneficial to the industry as silica is an abundant earth element. © 2020 IOP Publishing Ltd.