The present invention provides a method for manufacturing a diamond substrate, including: a first step of preparing patterned diamond on a foundation surface, a second step of removing a foreign substance adhered on a wall of the patterned diamond prepared in the first step, and a third step of growing diamond from the patterned diamond prepared in the first step to form the diamond in a pattern gap of the patterned diamond prepared in the first step. There can be provided a method for manufacturing a diamond substrate with few dislocation defects, in which generation of abnormal growth particles are suppressed.