Licorice root (Glycyrrhiza glabra L.) is a valuable medicinal raw material containing a complex of biologically active substances with antioxidant activity. Optimization of the extraction process allows to increase the efficiency of target components extraction. The aim of the study is to determine the optimal extraction parameters for maximum extraction of phenolic compounds and achieving high antioxidant activity of licorice root extracts. The Box-Behnken experimental design method with three factors was used to optimize the extraction process: extraction time (60-120 min), hydromodulus (1:10-1:30), and temperature (50-70°C). As responses, antioxidant activity was determined by DPPH method (FRSA, %), total phenolic content by Folin-Ciocalteu method (TPC, mg GAE/g), and dry matter yield (DM, %). Statistical data processing was performed with construction of mathematical models of response dependence on variable factors. Regression equations describing the dependence of antioxidant activity, phenolic content, and dry matter yield on extraction parameters were obtained. It was found that hydromodulus has the greatest influence on all studied responses. For antioxidant activity (Y1) and dry matter yield (Y3), the linear and quadratic terms of hydromodulus are determining. Total phenolic content (Y2) depends on extraction time, hydromodulus, and their interaction. Maximum antioxidant activity (16.4%) and highest dry matter yield (3.05%) are achieved at extraction time of 120 min, hydromodulus 1:10, and temperature 60°C. Optimal parameters for extraction of biologically active substances from licorice root were determined by experimental design method. The obtained mathematical models allow predicting qualitative characteristics of extracts depending on process conditions. The research results can be used for developing technology for obtaining standardized licorice extracts with specified properties.

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