A nucleation of intragranular ferrite grains by B1-type non-metallic inclusions was investigated using electron microscopes. Intragranular ferrite grains surrounding a TiN particle is observed in Ti-containing steel. On the other hand, no intragranular ferrite nucleated on NbN and ZrN. It is deduced that the NbN and the ZrN particle can not promote a nucleation of an intragranular ferrite for their high interfacial energy with ferrite. The TiN particle which has the BN relationship with the intragranular ferrite is an inclusion that effectively promotes an intragranular ferrite nucleation. The acicular ferrite grains formed in the austenite grains were trigged by the intragranular ferrite grain(s) formed around TiN.