In a method of forming a metal line and a method of manufacturing a display substrate, a channel layer and a metal layer are successively formed on a base substrate. A photoresist pattern is formed in a wiring area. The metal layer is etched by using the photoresist pattern to form a metal line. The photoresist pattern is removed by a predetermined thickness to form a residual photoresist patternon the metal line. The channel layer is etched by using the metal line to form an undercut under the metal line. The protruding portion of the metal line is removed by using the residual photoresist pattern. The protruding portion relatively protrudes by formation of the undercut. Thus, an aperture ratio is increased, an afterimage is prevented, and the display quality is improved.