Wellbore stability is of one of challenges in drilling industry. Shale formation is of one of the most problematic rocks during drilling because the rock has very low permeability and very small pores (nanometers). In this study, the viability of the Alumina nanoparticles in Water-Based Mud (WBM) is assessed. The effect of Alumina nanoparticles (alpha and gamma) as mud additives to improve the rheological properties in water- base drilling fluids are experimentally investigated. The Alumina nanoparticles has specific chemical and physical properties such as: high compressive strength, high hardness, high thermal conductivity, these properties improve the rheological properties of water base drilling fluid, reduce filtration loss and meet environmental regulations. The results of experiments indicated that Alumina nanoparticle are improving rheological properties such as: yield point (YP), gel strength (GEL 10s, Gel 10min) of water- base drilling, that can be used to improve the rheological and filtration properties of drilling fluids. The experimental data showed that, Alumina nanoparticle as a Nano additive, possessed excellent properties such as thermal stability, rheology enhancing, fluid loss control and lubrication. Also, it could plug the shale formation effectively and improve the pressure bearing capability of formation significantly. In addition, Alumina nanoparticles reduced 60% API/HPHT fluid loss by 60% in comparison with blank sample. The most striking feature is that shale integrity improved by Nano fluid between 60 and 70 percent in comparison with blank sample. Also, data experimental of CT Scan are shown that the filter cakes formed by each of the Nano-drilling fluid samples with alpha alumina and gamma alumina base are more cohesive and cause an integrated filter cake on the well.