This article investigated an atmospheric pressure dielectric barrier discharge (DBD) plasma reactor to explore the effects of carrier gas type, applied voltage and pulse repetition frequency on upgrading of 4-methylanisole as a lignin-derived bio-oil. A series of experiments were designed to realize the effects of argon (Ar) and hydrogen (H-2) on upgrading. The results showed that argon yields higher conversion of 4-methylanisole compared to hydrogen, and both voltage and frequency had positive effects on the conversion of 4-methylanisole. Increasing voltage and frequency led to an increase in the number of active species and subsequently, the number of effective collisions as a result 4-methylanisole conversion and discharge power (DP). In the experiments with applied voltage of 9 kV, frequency of 20 kHz and existence of Ar as carrier gas, the conversion reached to 29.80% at the DP of 77 W. The most abundant products were 4-methyphenol and 2,4-dimethylphenol, which were formed from transalkylation and hydrogenolysis reactions. It was found that the increase in the applied voltage, frequency and Ar percentage of carrier gas (as adjustable parameters), has the same effects on product distribution; since their variation resulted in the same changes in core plasma parameters such as electron energy, temperature and density. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.