Objectives: The idea is also the general objective of this work, which is to study the behaviour of Gallic acid as a simple phenol in physiological electrolytes, in simulated gastric acid and physiological phosphate buffer. In addition, it was necessary to select the electrode with best respond toward Gallic acid, the best sensitivity. The specific objectives of this work are to use the selected electrode to determine how reliably we can determine the concentration of Gallic acid by electrochemical methods and to evaluate the antioxidant activity of a substance. By comparing the obtained results with the results of the classical method, conclusions about the possibility of using voltammetric methods in the evaluation of antioxidant activity will be found. It is necessary to find a correlation between the results of electrochemical and spectrophotometric methods to make this method standard method for evaluation of total phenol and antioxidant activity. Material and Methods: A glassy carbon electrode was modified with singlewalled and multiwalled carbon nanotubes to improve electron transfer and increase sensitivity toward Gallic acid. Using aqueous extracts of selected plants, Gallic acid concentration was determined by differential pulse voltammetry. Using the same extracts, total phenolic and antioxidant activity were determined by classical spectrophotometric methods. Results: Analysis of the results showed that the electrode modified with singlewalled carbon nanotubes responded best to Gallic acid. Obtained sensitivity of 99 µA indicates very high sensitivity and excellent linearity (0.995) of the proposed method. The highest concentration of Gallic acid was observed in rosemary extract, 10700 μg GAE/L, or 171.2 mg/kg dry mass. The lowest concentration of Gallic acid was observed in Matcha powder extract. The highest level of total phenols by the spectrophotometric method was observed in the rosemary extract, while the highest antioxidant activity by the FRAP method was measured in the sage extract. Conclusions: The electroanalytical method presented in this work can be used for the rapid determination of total phenols in dry extracts of herbs and, consequently, for the determination of antioxidant activity. The results of this work can significantly contribute to the development of a new method for the determination of Gallic acid, or for the determination of total phenols in plant material, which is also an advance in the development of voltammetric methods for the determination of antioxidant activity of various compounds.