The aim of the present study was to determine the anticonvulsant effects of xanthotoxin (8-methoxypsoralen) isolated from the fruit of Pastinaca sativa L. This plant is used in European traditional medicine, including Poland. For this purpose, high-performance counter-current chromatography was used. Different solvent systems, mixtures of n-heptane, ethyl acetate, methanol and water were tested in order to calculate partition coefficients. Finally, a mixture with the ratio of 1:1:1:1 (v/v/v/v), giving the K value = 0.92, was chosen as optimal. A rapid scale-up process from analytical to preparative was developed. Evaluation of the anticonvulsant action of xanthotoxin in the mouse maximal electroshock-induced seizure test revealed that it produced a clear-cut anticonvulsant action in mice, and the experimentally-derived median effective doses (ED50 values) ranged between 219 and 252 mg kg−1.