Abstract: To investigate the impact of lithologic differences in the hilly regions of Southeast China on the rainfall thresholds for landslides, this study quantitatively compares the rainfall-threshold curves and parameter differences between quartz schist and granite zones based on the clustered landslide event in Nanping City on 28 June 2021. The TRIGRS model was used to investigate slope stability under 460 rainfall scenarios. Rainfall-threshold curves were constructed for the two lithologic zones, and model performance was validated using the %LRclass metric. The results show that the critical rainfall intensity in the quartz schist zone is generally lower than that in the granite zone. The threshold-curve parameters α and β exhibit a significant negative correlation. With increasing slope gradient, α decreases monotonically and β increases in the quartz schist area, whereas in the granite area α increases first and then decreases, and β decreases first and then increases. Numerical results of pressure head indicate that differences in the saturated hydraulic conductivity of the overlying soil layer are the key factor driving the distinct slope-gradient-dependent responses of rainfall thresholds in the two zones. This study reveals lithology-controlled differences in rainfall thresholds and provides a methodological and technical reference for further investigation on regional rainfall-induced landslide early warning.