The electronic structure of typical perovskite-type hydrides, MMgH3 (M=Na, K, Rb), CaNiH3 and SrPdH3, are simulated to understand the nature of the chemical bond between constituent ions in them using the DV-Xα molecular orbital method. For MMgH3, it is found that the valence band consists mainly of the H 1s and Mg 3s, 3p components, and the M s, p components are distributed over the empty conduction band. Thus, the covalent bond still remains between Mg and H ions, but the ionic bond is rather strong between them. The chemical bond between M and H ions is further ionic in character. On the other hand, for CaNiH3 and SrPdH3, covalent bond is dominant between Ni (or Pd) and H ions. Also, the enthalpy change in the dehydrogenation reaction, ΔH, is estimated for several reaction paths, using the plane-wave pseudopotential method. For example, in the NaMgH3 system, ΔH is estimated to be 72.9 kJ/molH2 in the reaction, NaMgH3→NaH+Mg+H2, and 82.6 kJ/molH2 in the reaction, NaH→Na+1/2 H2. In agreement with these calculated results, NaMgH3 dehydrides in these two-step reactions at about 673 K according to recent experiments.