Abstract: Quantitative risk assessment of slope failure is an important prerequisite for formulating rational strategies for landslide risk mitigation and developing landslide risk-based warning system. However, the risk of slope failure in two-dimensional (2-D) spatially variable soils cannot be effectively evaluated. This paper aims to propose an efficient approach for quantitative risk assessment of slope failure considering 2-D spatial variability of soil properties in the framework of Monte-Carlo simulation (MCS) and limit-equilibrium analysis of slope stability. The proposed approach comprising of 2-D spatial variation modeling of soil properties, stability analyses of spatially variable soil slopes, identification of representative slip surfaces and quantitative risk assessment of slope failure is described. The failure risks of a two-layered soil slope example under three cases are investigated to demonstrate the effectiveness of the proposed approach. The results indicate that the proposed approach has the following advantages:1) it can effectively identify the representative slip surfaces (i.e., key failure modes) of spatially variable slopes; 2) it can produce accurate risk of slope failure with much less computational efforts and provide an effective means for quantitative risk assessment of slope failure at low-probability levels in 2-D spatially variable soils; 3) it can quantify the contributions of each key failure mode to the probability and risk of slope failure, and hence provide an important reference for landslide risk mitigation measures.