Abstract: In this paper we have calculated the electronic structures of the cyclic nucleotides cAMPand cGMPby means of the CNDO/2 method. On basis of the computed charge distributions in the molecules the possible interaction mechanism between the mentioned nucleotides and protein kinase has been discussed. We have showed that in this interactions the essential part perhaps is the sugar-cyclic phosphate one, and it includes electrostatic interactions of both 3' and 5' and exocyclic oxygen atoms and also the hydrogen bond interactions of oxygen atoms O3', O5' and O2'. At the same time, we have also discussed the possible actions of bases in regulating activity of two cyclic nucleotides. In addition we have analyzed some hydrogen bonding in both nucleotides cyclic cAMP and cGMP.