The response reduction factor (R) is used in seismic design to account for nonlinear response of structures. Significant research efforts have been made to obtain R factor for buildings. Various national codes recommend R values depending on structural configurations and construction details mainly for buildings on flat grounds. However, studies on R factor for buildings on hill slopes are not available. The present study focuses on the nature of R factor of building resting on slopes considering the effect of irregularities due to slope. Based on extensive regression study of nonlinear static pushover (NSP) analysis results, an attempt has been made to explore the possibility of obtaining a modification to estimate the R factor. The results show a good agreement with the R values obtained from the actual NSP analysis results. The various statistical parameters used for validation of a regression model support the prediction capability of the anticipated relation.