An analysis of the molecular orbital wave function from the viewpoint of resonance theory is proposed. This is an extension of our previous method to treat the conjugated-electron system. It enables us to calculate the weights of resonance structures being consistent with the Mulliken population as well as bond order analysis. The method has been applied to LiH, H2O, butadiene, and the S(N)2 reaction. (C) 2011 Elsevier B.V. All rights reserved.