Abstract: The microstructures of La deoxidized steels obtained at different cooling rates were investigaled by optical microscopy and scanning electron microscopy coupled to an energy dispersive X-ray spectrometer. The continuous cooling transformation diagram of the tested steel was also drawn in this paper. It is found that in the cooling rate range of 4 to 10℃·s^-1, intragranular ferrite can form in the steel. While at the cooling rate of 8℃·s^-1, the microstructure mainly consists of fine and dispersed intragranular acicular ferrite (IAF). The lattice disregistry between lanthanum-containing inclusions and α-Fe is small; especially, this value of La₂O₂S is 0.2%. These kinds of inclusions can induce IAF nucleation and sympathetic nucleation, and also make grains refined.