Background: An accurate, simple and selective UV-spectrophotometric method was developed for the estimation of silicon in medicinal plant raw material - horsetail herb (Equisetum arvense L.) of Russian origin. Methods: The determination of total silicon content in terms of silicon dioxide (SiO2) by the direct ultraviolet-visible (UV-Vis) spectrophotometry method (at a wavelength of 815 ± 5 nm) in the horsetail herb is based on the formation of yellow-colored silicomolybdic acid, and its further reduction to molybdenum blue. Results: Recoveries were found to be in the range of 100.2 to 105.1% and %RSD was less than 2%. Conclusion: The developed method is accurate, specific, precise within an interval 2-12% and suitable for the analysis of horsetail herb commercial samples. © 2019 Phcogj.Com.