This paper presents an electron microscopy study of reduced calcium titanate crystals (CaTi₂O₄) and the growth mechanism of titanium monoxide TiO_xon a CaTi₂O₄surface. Large high-quality CaTi₂O₄crystals were prepared using the molten salt flux method. The crystallographic directions and the growth direction of the CaTi₂O₄crystalline needles were confirmed by electron backscatter diffraction and Kikuchi pattern analysis. The low-angle grain boundaries in CaTi₂O₄and the crystallographic orientation relationship between CaTi₂O₄and TiO_xwere investigated using high-resolution transmission electron microscopy. It is found that both the low-angle boundaries and the amorphous area may play a key role during the growth process of titanium monoxide TiO_x. The results presented here contribute to a better understanding of the detailed growth mechanism of TiO_xon a CaTi₂O₄surface.