Microstructural studies on (1 - x)Ba(Mg1/3Nb2/3)O-3-xCa(Mg1/3Nb2/3)O-3 (BCMN) complex perovskite compounds, which are mixtures of Ba(Mg1/3Nb2/3)O-3 (BMN) and Ca(Mg1/3Nb2/3)O-3 (CMN), were conducted using scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. Pure BMN and CMN both have a 1:2 ordered structure, via the chemical ordering of B-site cations; however, the tilting of oxygen octahedra is involved in pure CR;IN, whose structure has a 1:2 ordered monoclinic unit cell that is characterized by (+/-1/6,+/-1/6,+/-1/6)-type superlattice reflections in electron diffraction patterns along the [110] zone axis that is based on a simple cubic perovskite. Studies of the morphologic differences have indicated two types of inhomogeneities in a mixture of the BCMN system: (i) a rather large-scale segregation (i.e., grain sizes of several micrometers), where the grains are separated compositionally as being barium-rich or calcium-rich, and (ii) fine scale lamellar-type segregations 20 mn wide and 200 mn long. The segregation that is caused by Ba and Ca ions can be identified by the difference of superlattice modulations from high-resolution transmission electron microscopy lattice images.