The present invention provides a method for manufacturing a nitride semiconductor self-supporting substrate and a nitride semiconductor self-supporting substrate manufactured by this manufacturing method, the method including at least: a step of preparing a nitride semiconductor self-supporting substrate serving as a seed substrate; a step of epitaxially growing the same type of nitride semiconductor as the seed substrate on the seed substrate; and a step of slicing an epitaxially grown substrate subjected to the epitaxial growth into two pieces in parallel to an epitaxial growth surface. As a result, there is provided a method for manufacturing a large-diameter nitride semiconductor self-supporting substrate having an excellent crystal quality and small warp with good productivity at a low cost, etc.