An improved ASCE/SEI 7–10 ground-motion scaling procedure for three-dimensional (3D) response history analysis (RHA) of buildings is presented. In this procedure, different scale factors for two horizontal components of the ground motion are used, and their spectral shapes are considered in ground-motion selection stage. The accuracy of the improved procedure is evaluated by utilizing 3D models of nine asymmetric-plan buildings. It is demonstrated that the improved procedure provides on average 15% conservative estimates of engineering demand parameters while the original version underestimates them on average 29%. Thus, the improved ground-motion selection and scaling procedure is found to be appropriate for nonlinear RHAs of multi-story plan-asymmetric buildings.