We report on the fragmentation dynamics of triply charged, diatomic, molecular ions of N O and CO. Dissociative fragmentation after multiple ionization of N O and CO is studied under the impact of 200 keV proton beam using recoil-ion momentum spectrometer. Kinetic Energy Release distributions (KERDs) for various fragmentation channels were obtained. We have also calculated the potential energy curves (PECs) for ground and several excited states of N O 3+ and CO 3+ molecular ion. The obtained KERDs are discussed in the background of the calculated PECs as well as the simple Coulomb excitation model. Coulomb breakup of the unstable precursor molecular ion shows a clear preference for the N 2+ + O + (and C 2+ + O + ) fragmentation channel.