This paper aims at deriving partial factors for soil strength parameters for the new Egyptian geotechnical design code that is based on the Limit State Design (LSD) method. It deals with the slope stability problem which is of a major concern for both the slope instability, and the Ultimate Limit State (ULS) of the overall stability that is applicable to many geotechnical applications. In the present study, the determination of the partial factors is mainly based on probabilistic methods in order to reflect the different levels of variability for the different soil strength parameters. Firstly, the levels of reliability, in terms of the Probability of Failure (Pf) or the equivalent reliability index ( ) resulted from the Global Safety Factors (GSFs) given in the current Egyptian code, are examined. In order to get a considerable safety margin that considers the different levels of variability of soil strength parameters, a target reliability index ( T) is then proposed. This index is determined based on a practical range of Coefficient of Variation (COV) for strength parameters, the current practice, and the values given in international codes. Partial factors for strength parameters are then calibrated based on probabilistic methods such as the First-Order Reliability Method (FORM) and the Monte Carlo Simulation (MCS) method to achieve the chosen target level of reliability index, T.