With the increasing cleanliness of steels in recent years, it has made possible for making micro-alloyed steels with rare earth elements. It is found that the addition of rare earths has a significant effect on the solid-state phase transformation behavior of steels, especially for low-carbon low-alloy steels. The effectiveness in modifying the inclusions and inducing nucleation by RE addition has been studied intensively and approved substantially. Whereas, the micro-alloying effect of RE on the ferrite phase transformation of steel is still unclear. The effect of rare earth elements (RE) on austenite-ferrite transformation temperature during continuous cooling, and the isothermal transformation kinetics of Fe-C alloys and Fe-C-Si-Mn low carbon steels has been investigated in this article. It is found that a tiny amount of RE addition can reduce the starting point temperature of proeutectoid ferrite during continuous cooling. Additionally, the addition of RE also changes the ferrite transformation kinetics in the isothermal process: for Fe-C-(RE) alloys, the addition of RE slows down the transformation rate during the whole transformation process due to the pinning carbon diffusion effect; For Fe-C-Si-Mn alloys, RE elements can play a double role of pinning carbon diffusion and changing grain boundary energy, and then prolong the incubation period and decreases the rate of phase transformation during the initial stage, while increase the phase transformation rate during the middle and late of phase transformation.