Crystal structures of ilmenite type NaNbO₃ and LiNbO₃, which were prepared by low temperature hydrothermal and ionexchange reactions respectively, were refined by the X-ray powder Rietveld method. Final R-factors were R_wp=16.9, R_p=12.2, R_B=6.1% for NaNbO₃ and R_wp=13.9, R_p=11.1, R_B=5.7% for LiNbO₃. The mean Nb-O distances of both ilmenite type compounds agreed with those of their corresponding stable phases. The mean Na-O distance of the ilmenite type NaNbO₃ was as large as that of the spinel type Na₂WO₄, while, the mean Li-O distance in the ilmenite type LiNbO₃ was slightly larger than that of the LiNbO₃ type LiNbO₃ or other compounds containing LiO₆ octahedra. Structural refinement of other ilmenite type compounds of MgTiO₃, CdTiO₃, NaSbO₃, NaBiO₃ and KSbO₃ was also carried out by the X-ray powder Rietveld method. Stability field of ilmenite type compounds, ABO₃, was discussed on the basis of volumes of the AO₆ and BO₆ octahedra.