The surface polarity of organically functionalized cellulose fibers has been characterized with linear solvation energy relationships. The Kamlet-Taft hydrogen-bond-donating ability, the hydrogen-bond-accepting ability, the dipolarity/polarizability, Gutman's acceptor number (an indicator of the electron-accepting ability), and Reichardt's E-T(30) parameter have all been used to quantitatively represent the polarity of the chemically treated and untreated fiber surfaces. Three different probe dyes, cis-dicyanobis(1,10-phenanthroline)-iron(II), Michler's ketone, and aminobentodifuranone, have been used as indicators to measure the polarity with correlation analysis of the energy of the ultraviolet-visible absorption maxima. Solvatochromic methods have been proven to be effective in characterizing chemically modified lignocellulosic fibers. Different silanes, NaOH, and long alkyl groups, used to modify the cellulose fiber surface, have changed the hydrogen-bond-donating ability of the fiber.