<p>As a rock mass characterization system, Geological Strength Index (GSI) system is widely used in different rock engineering applications due to its use in the Hoek Brown failure criterion. However, the saturation condition, which has an effect on geomechanical properties of both rock material and discontinuities, has not been considered in the GSI system. The main purpose of this study is to examine the saturation effect in the GSI system. In order to take the saturation effect into account within the GSI system, a correction factor was proposed using the Barton failure criterion in this study. Multivariate regression analysis was also carried out to predict the correction factor for saturated conditions. The proposed equation derived by multivariate regression analysis was found statistically reliable. A modification was suggested for the process of determining the GSI value using the correction factor. Hoek Brown failure envelopes were drawn using the corrected and uncorrected GSI values to examine the effect discontinuity saturation on rock mass strength. In order to check the extent of saturation effect on rock engineering applications, stability of a rock mass slope was also examined. The results of slope stability analyses showed that the factor of safety value will be considerable higher than the actual value without using proposed corrected GSI value.</p>