In order to investigate the effects of the microstructure and chemical compositions on the hole expansion property of C-Mn steels, four C-Mn steels were used and heat treated into different structures. The influences of the tensile properties on the hole expansion property were also investigated. It has been found in this paper that C-Mn steels with a high ratio of yield strength to ultimate tensile strength usually have a good hole expansion property. A high silicon content in solid solution can improve the hole expansion property. Carbon has a significant detrimental effect on the hole expansion property. (C) 2003 Kluwer Academic Publishers.