Abstract The Cation Exchange Capacity (CEC) of the Nigerian bentonitic clay samples obtained from the North Eastern Nigeria, namely:Garin Hamza, Pindiga, Tongo, BulabulinMaiduwa and SabonGarinNgalda were investigated using Methylene Blue method. The raw samples were beneficiated using wet beneficiation method to reduce the excess silica content and further activated with Na2CO3 to become Sodium based bentonite used for drilling fluid formulation.The CEC values for raw Nigerian Bentonitic clay samples ranges from 12 to 44 meq/100 g which have low values compared to standard (57.9 meq/100g). The CEC values significantly increased compared to the raw samples after silica (Quartz) reduction between 31.3 to 46.0meq/100g. The CEC values remain relatively the same even after activation with Na2CO3, except Tongo bentonite with CEC value of 38.9 meq/100g for raw bentonite that reduced to 34.9 after silica reduction but on activation with Na2CO3 the value rose to 39.7 meq/100g. It was generally observed that the CEC values of all the formulated drilling fluid for the treated samples slightly reduced due to the effect of the viscosifier (Poly anionic cellulose) used during formulation.