Abstract: This paper describes non—degenerate perturbational molecular orbital theory and its some uses. First order and second order perturbational basic formula, atom—atompolarizability, atom—bond polarizability, bond—bond polarizability and the δE, δq, δP calculative method of perturbational system are presented. The PMO program being lapplied to the TRS-80 microcomputer system is worked out. The calculated data of benzene and naphthalene with respect to this method are similar to those described in the article published by H. Kato. It is suggested that this program could be used for calculation of conjugate system on research in structure-activity relationships of related drugs.