Probabilistic approach of slope stability analysis has recently become the focus of attention of many researchers in the field of Geotechnical Engineering.This research presents a study to investigate the suitability of an expedient technique to search for the critical probabilistic slip surfaces and the associated minimum reliability indexes of earth slopes. The proposed technique is based on the Ordinary Method of Slice (OMS) as a stability model in combination with First-Order Reliability Method -I (FORM-I) as the reliability model. The Sequential Unconstrained Minimization Technique (SUMT) of solving constrained minimization problems has been used coupled with the above as the numerical scheme for minimization of the reliability index function. Using First-Order Reliability Method (FORM), with the help of a developed computer program based on the FORM in conjunction with the OMS, a few numerical example problems have been solved and some important observations have been made.