The pre-functionalization of organic ligands before MOFs synthesis has been widely carried out via wet-chemical methods. A possible novel route to perform the pre-functionalization of MOFs’ organic ligands is to graft amino groups on the ligand by means of plasma treatments. In this study, a NH3 impulse dielectric-barrier discharge plasma treatment is used to investigate the efficiency of the pre-functionalization of terephthalic acid. For this purpose, plasma diagnostics is coupled with material characterizations to identify the main reactive plasma species involved in the ligand functionalization. The presence of NH radicals in the plasma phase together with structural modification evidence the effect of the plasma treatment. Chemical analyses of the treated material confirm the presence of nitrogen in the treated sample and prove that the grafting of the amino group occurs at the functional carboxyl group (-COOH) of terephthalic acid, by substituting the C–OH bond by C–NH2 bond. All these results indicate successful modification of terephthalic acid by grafting amino groups thanks to the plasma treatment.