Interests in the design of water-based muds(WBM) have escalated due to wellbore instability issues that arise from the abundance of problematic shales encountered while drilling. Conventional water-based muds(WBMs) that are used to drill through water sensitive shale formations cause a high degree of wellbore instability. Consequently, oil based muds(OBMs) were adopted to solve the wellbore instability problems due to their superior shale stabilization properties. Unfortunately, high costs, environmental restrictions, cuttings and used mud disposal difficulties and safety have largely limited the use of OBMs. As a result of these challenges with OBMs, WBMs that have the ability to effectively reduce shale instability problems have once again come under the lime light to replace the OBMs. Potassium-based (KCL)muds are used in areas where inhibition is required to limit chemical alteration of shales. This research study therefore was undertaken to evaluate the inhibition effects of different concentrations of KCL on the rheological properties of water-based mud(WBM) contaminated with shale. The rheological values using FANN viscometer with different concentrations of KCl((0.2%, 0.4%,1.0%,2.0% and 4.0%) respectively by weight of contaminated 8.5PPG WBM with typical shale sample from the Niger Delta Region of Nigeria were evaluated. Test results indicated that the KCl inhibited the swelling tendencies of the shale and the rheological values reduced drastically. The reduction in rheological values considering the 600rpm reading were 0%, 36%, 60%, 94% and 181% respectively compared to results without KCL in the mud as indicated above. Therefore, to avoid non-productive time resulting from hole instability problems caused by shale, when drilling is expected to encounter shale zones, proper design of the drilling fluids using WBMs with KCL that will inhibit shale swelling is imperative.