Abstract: The high temperature ductility of samples, taking from a Q345B continuous casting slab in the transverse direction, drawing direction, vertical direction and at the central part, as well as an AH32 continuous casting slab at the surface and 1/4 thickness position, was investigated by using a Gleeble-1500 testing machine. The fractographs and microstructures of high-temperature tensile samples were observed by optical microscopy and scanning electron microscopy. Experimental results show that the high temperature ductility below 950℃ changes little between 4 groups of different samples from the Q345B slab, but the variation tendencies of high temperature ductility above 950℃ are greatly different. The changes of high temperature ductility of 3 groups of samples from the AH32 slab at the surface are the same, and the reduction of area has little fluctuation. Whereas the high temperature ductility of 3 groups of samples at the 1/4 thickness differs entirely from that at the surface, and the reduction of area appears fluctuant greatly. The reason is that microcracks, composition segregation, porosity and looseness occur more easily in the columnar crystal zone of sampling than in the equiaxed crystal zone of the surface.