Purity steel containing La was investigated by means of metallographic analysis and transmission electron microscopy (JEM2010). The result showed that the effect of solution La on γ→α phase transformation was remarkable. Element La refines the ferrite grains. During the quenching in the iced brine, La makes γ→α transformation proceed according to massive transformation mechanism. The ferrite grain boundary is irregular. The ferrite grain is massive, sheetlike and acicular. La promots the formation of massive structure.