Isomeric ratios of isomeric pairs produced by photonuclear reactions (γ, n) on Se, Ce, Eu and Hg targets induced by bremsstrahlung with endpoint energies in the giant dipole resonance region have been theoretically calculated using TALYS 1.95 code in combination with Geant4 simulation. The computed isomeric ratios as a function of the bremsstrahlung endpoint energies in the range of 10 to 25 MeV resulted from convolution between calculated differential cross-sections using six level density models available in TALYS 1.95 and the bremsstrahlung spectra simulated by the GEANT4 toolkit. Moreover, for each level density model, eight gamma strength functions have been employed. The calculated results are compared to the experimental data in the existing literature for Talys 1.95 model evaluation.