Abstract: 1,3-Dipolar cycloaddition reaction between 3-oxidopyrazinium and methyl acrylate has been studied both experimentally and theoretically. Structures of the obtained cycloadducts, exo and endo isomers, were characterised based on spectral data namely IR, 1H and 13C NMR. These reactions can be interpreted in terms of the classical 1,3-dipolar cycloaddition reaction of 3-oxidopyridinium. Moreover the observed cycloaddition reaction has been investigated theoretically by means of the Hartree-Fock method using 6-31G as the basis sets in the gas phase in order to have more insight into their reaction profiles. All the geometries on the reaction paths have been optimised and the transition state structures have been ascertained by frequency analysis. Since the synthesis has been carried out in acetonitrile, the optimised structures have been used for single point computationin this solvent using the density functional method with B3LYP as the functional. The computations have allowed the determination of the activat on energies and enthalpy changes of the reactions. These have been used for the interpretation of kinetic and thermodynamic stabilities. It is generally found that the addition reactions have lower activation energy and enthalpy changes in acetonitrile compared to the gas phase.