Diluted effect on the charge ordered (CO) structure in dielectric materials LuFeMO 4 (M = Cu, Co) were investigated by an energy-filtered transmission electron microscopy (TEM), in combination with a conventional TEM. It is revealed that partial substitution of Cu 2 + and Co 2 + for Fe 2 + in LuFe 2 O 4 destabilized the CO structure. In LuFeCuO 4 , there exist characteristic zigzag-shaped diffuse streaks and diffuse spots at the h/3-δ h/3-δ 0-type positions (h: integer, δ = 0.06) in reciprocal space, which originate from static cationic ordering of Fe 3 + and Cu 2 + ions in the triangular lattice. Moreover, real-space images by the energy-filtered TEM revealed that nanometer-sized domain structures with the 5∼10 nm size are formed. In contrast, honeycomb-shaped diffuse streaks were found in LuFeCoO 4 , in which no domain structures are observed in real-space images.