Abstract: Radial cracking occurred in the main mill roll in a wheel rolling after a very short service time. The cracking causes of mill roll were analyzed by means of chemical composition analysis, hardness test, macro examination, fracture analysis and metallographic examination. The results show that the chemical compositions of the cracked mill roll did not meet the requirements of internal control, poor microstructure, such as severe dendrite segregation, uneven graph ite size, abnormal nodularizing graphite shape, few and uneven carbides, local carbides network etc, and there were loose defects near the working face. The improper chemical compositions, poor microstructure and internal defects make the hot crack resistance and thermal fatigue resistance of the mill roll decreased, which led to the cracking failure of the mill roll in a very short service time.