We have performed an ab initio band structure calculation for the new high- T c related iron-pnictide compounds LaFeXO (X = P, As), BaFe 2As 2, CaFe 2As 2 and LiFeAs (X = P, As). We found that LaFeXO and CaFe 2As 2 have many similarities in their band structures, which is expected by an ionic model. We found that the degree of distortion of FeAs 4 tetrahedra in LaFeAsO considerably changes the slope of the density of states near the Fermi level, and this result may explain why REFeAsO (RE = Nd, Sm, …) have higher T c than LaFeAsO when electrons are doped. For all the above compounds, the density of states at the Fermi level decreases when X atoms approaches to the Fe–Fe plane, which means that the hybridization between Fe and X orbitals considerably expands the Fe d-bands.