Abstract: An endodontic stop positioner combined with a reamer or a file used for taking a measurement of the root canal length of the tooth, includes a positioning body with a hard member and a soft member made of non-metal material, a central penetrating hole formed in the positioning body for accomodating the reamer or file, which reamer or file is movably held in the central penetrating hole for being inserted into the root canal of the tooth in taking the measurement in an X-ray, and at leat a wire disposed in a bottom center of the hard member and located in perpendicular intersection with the reamer or file. Consequently, the intersection point between the wire and the reamer or file can be clearly indicated in the X-ray for accurately measuring the root canal length of the tooth therewith.