In this study, the direct pair production of the pseudoscalar Higgs boson at a gamma gamma collision is analyzed in the context of the two Higgs doublet model (THDM), taking into account the complete one-loop contributions. In order to illustrate the effect of the new physics, four benchmark point scenarios, which are consistent with theoretical and current experimental constraints, are chosen in the type-I THDM with an exact alignment limit. The effect of individual contributions from each type of one-loop diagram on the total cross-section is examined in detail. The dependence of the cross-section on the center-of-mass energy is also presented at the various polarization configurations of the incoming photons. Moreover, the regions m(12)(2) - tan beta and m(A) - tan beta in the parameter space of the THDM are scanned for some fixed values of other parameters. The box-type diagrams make a much bigger contribution to the cross-section than the others at high energies. The total cross-section can be enhanced by a factor of two thanks to opposite-polarized photons as well as threshold effects.