The J-integral has been used as a fracture criterion for elastic-plastic behavior of metals. It may be pertinent to use the JIc concept for design or nondestructive inspection of rotating disks which have crack-like flaws and exhibit some amount of plastic behavior to fracture. JIc for cracked rotating disks of rotor forging steel is determined experimentally and is compared with that obtained using compact specimens. It is shown that prediction based on the compact tension tests agrees well with initiation of crack growth in rotating disks.