Abstract: The charge distributions of various acids and their conjugate bases arc calculated by using CNDO/2 and MNDOwith full geometry optimization. The deprotonalion energy is found to be better correlated with the charge on the acidic hydrogen than with the charge on the atom linking to the hydrogen and with the charge on the neucleophilic atom of the conjugate base. This shows that the charge on the acidic hydrogen has an important effect on acidity, whereas the effect of the charge on the linking atom and on the neucleophilic atom of the conjugate base is not imporant. It can thus be deduced that the view of stabilization of the anion due to spreading the negative charge is not the significant explanation of acidity.