Quantum Chromodynamics (QCD) is the theory of strong interactions. Since the exact form of confinement of quarks from QCD is not known constituent quark modes were developed incorporating the basic features of the QCD. Mesons are the very fundamental particles in hadron physics. Hence, a deep understanding of the internal structure of the mesons is of crucial importance for explaining properties concerning more complex systems. In this work, non-relativistic and relativistic constituent quark models have been developed including instantons as a short range nonperturbative gluonic effect. The total energy or the mass of the meson is obtained by calculating the energy eigen values of the Hamiltonian in the harmonic-oscillator basis.