Elimination of unwanted electrostatic charges created by charging mechanisms of insulating materials (contact or friction) is an important step for the proper operating of most industrial applications as well as for the safety of individuals, due to the many problems caused by these charges. However, achieving the best performance of the process depends mainly on the quantity of these charges in some other applications, which requires enhancing them. In this context, surface plasma modification of granular insulating materials using Dielectric Barrier Discharge (DBD) is an effective technique for enhancing triboelectric charging. The aim of the present work is to find the optimum tribocharging process for DBD-treated Polypropylene (PP) mm-size plastic granules by the design of experiments methodology, using MODDE 8.0 software. The effects of the applied voltage amplitude and the frequency have been investigated. The untreated and the DBD-treated granules were charged by triboelectric effect in a vibratory device for 4 min. The triboelectric charge was measured using a Faraday pail connected to an electrostatic electrometer. The obtained results indicate that the both studied factors have very significant effects on the acquired charge. The optimum conditions for the charging process of DBD-treated granules correspond to an applied voltage of 27 kV for a frequency of 600 Hz; where the triboelectric charge has been optimally enhanced by about 20% compared to that of untreated granules.