Provided is a method of inspecting the back surface of an epitaxial wafer, capable of detecting pin mark defects in the back surface of the epitaxial wafer and quantitatively evaluating the defect size of individual point defects of the pin mark defects. The method of inspecting the back surface of an epitaxial wafer includes an imaging step of consecutively taking partial images of the back surface while moving the optical system using the scanning unit; an acquisition step of acquiring a full image of the back surface from the partial images; a detection step of detecting, in the full image, pin mark defects constituted by a set of a plurality of point defects present in the back surface of the silicon wafer 1; and a digitalization step of digitalizing the individual point defects to calculate the defect area of the individual point defects of the detected pin mark defects.