We report the production of ultracold heteronuclear NaCs molecules in excited electronic states by photoassociation (PA) of ultracold Na and Cs atoms. The saturation of the photoassociation scattering probability is observed from the dependence of the trap loss probability on the photoassociation laser intensity. Based on the scattering theory, we estimate the saturation intensity of photoassociation, which is deduced by fitting the experimental data to a saturation model.