In the last time, epigenetics is among top disciplines in the field of medicine research because epigenetic modifications of nucleic acids are associated with certain diseases and dysfunctions (e.g. human carcinomas – lung, thyroid, prostate and pancreas tumors-, leukemia, etc.). One of several epigenetic mechanisms that cells use to control gene expression is DNA methylation and one of different methylated guanines, N7- methyl G is recognized as the biomarker of DNA methylation. In the present study, electrochemical oxidation of methylated guanines (1N-, 7N- and 9N- derivatives) is studied to ascertain the relationship between the position of methyl group and the corresponding oxidation behavior. For this reason, the oxidation processes of methylguanines (methylGs) in the dependence on pH and the position of methyl group in the guanine molecule (pyrimidine ring vs. imidazole ring) were investigated. It was found that methylation has significant influence on the oxidation processes of methylGs and their oxidation is easier in the case of CH3- substitution at the pyrimidine ring than at imidazole one. Pencil graphite electrode (PeGE) was used as a working electrode throughout the study, since voltammetric signals of methylGs were poorly defined at conventional carbon electrodes, such as glassy carbon or HOPG.