The present invention relates to a polishing composition for a semiconductor wafer which is excellent in polishing property, and a polishing method. The polishing composition for a semiconductor wafer comprises colloidal silica consisting of non-spherical silica particles having a ratio of long axis to short axis of 1.5 to 15. The polishing method for a semiconductor wafer uses the polishing composition. The polishing composition can provide a remarkably high polishing rate compared with a polishing composition using spherical colloidal silica, and can provide good mirror-polishing without causing scratches. In addition, small alkali metal content enables reduction of adverse effects on a semiconductor wafer, such as residual abrasives after polishing.