This is a case of the core reamer breakage during anterior cruciate ligament reconstruction using bone-patellar tendon-bone autograft. A 19-year-old man with acute anterior cruciate ligament rupture had reconstruction surgery. During tunneling in the proximal tibia, the core reamer have been cracked open and broken. Rest of the procedure was performed routinely except the tibial sided fixation of bone block which was performed with larger interference screw than usual. The patient followed the accelerated rehabilitation program. The result was satisfactory at 2 years after surgery.