Sweet Chestnut (Castanea sativa Mill.) wood extracts, rich in Hydrolyzable Tannins (HTs), are traditionally used in the tanning and textile industries, but recent studies suggest additional uses. The aim of this work is the HPLC-DAD-ESI-MS characterization of Sweet Chestnut aqueous extracts and fractions obtained through a membrane separation technology system without using other solvents, and the evaluation of their antioxidant and antiradical activities. Total tannins range between 2.7 and 138.4 mM; gallic acid ranges between 6% and 100%; castalagin and vescalagin range between 0% and 40%. Gallic Acid Equivalents, measured with the Folin-Ciocalteu test, range between 0.067 and 56.99 g/100 g extract weight; ORAC test results for the marketed fractions are 450.4 and 3050 µmol/g Trolox Equivalents/extract weight. EC₅₀ values, measured with the DPPH test, range between 0.444 and 2.399 µM. These results suggest a new ecofriendly and economically sustainable method for obtaining chestnut fractions with differentiated, stable and reproducible chemical compositions. Such fractions can be marketed for innovative uses in several sectors.