Solid-state compatibility and melting relationships in the subsystem Al2O3-MgAl2O4-CaAl4O7 were studied by firing and quenching selected samples located in the isopletal section (CaO . MgO)-Al2O3. The samples then were examined using X-ray diffractomtery, optical microscopy, and scanning and transmission electron microscopies with wavelength- and energy-dispersive spectroscopies, respectively. The temperature, composition, and character of the ternary invariant points of the subsystem were established. The existence of two new ternary phases (Ca2Mg2Al28O46 and CaMg2Al16O27) was confirmed, and the composition, temperature, and peritectic character of their melting points were determined, The isothermal sections at 1650 degrees, 1750 degrees, and 1840 degrees C of this subsystem were plotted, and the solid-solution ranges of CaAl4O7, CaAl12O19, MgAl2O4, Ca2Mg2Al28O46, and CaMg2Al16O27 were determined at various temperatures. The experimental data obtained in this investigation, those reported in Part I of this work, and those found in the literature were used to establish the projection of the liquidus surface of the ternary system Al2O3-MgO-CaO.