The ordering in the assembly of biaxial molecules which interact pairwise via the dispersion force is investigated statistical-mechanically, where four kinds of liquid crystalline phase and phase transitions between some pairs of those phases are discussed in comparison with the existing theoretical results from the model of uniaxial molecules. There appear one uniaxial nematic phase, two kinds of biaxial nematic phase and one discotic phase. The phase diagram of temperature versus interaction strength are obtained, where the four phases mentioned above appear in different regions depending on the molecular shape. Some advantages of the present method in investigating the orientational ordering in biaxial liquid crystals, including the discotic phases, are discussed.