The elongation and the strength of rolled steel are severely affected by cracks in production. Reduction of cracks is important for the improvement of slab quality. In this paper, a series of experiments on internal crack healing in slab during rolling was carried out on the experimental rolling mill. The crack shape and the fracture morphology of the crack healing zones were observed by using the scanning electron microscope, and the shear strength of crack healing zone was tested through the tensile testing machine. With increase of the reduction ratio during rolling, the crack healing degree increases. © (2011) Trans Tech Publications, Switzerland.