The measurements of the contact angle were made for water, glycerol, formamide, diiodomethane and bromoform on a cassiterite surface covered with a mixed film of SDS and TX-100 formed by adsorption from solution of SDS and TX-100 at different molar fraction at a constant concentration equal to 2 x 10(-4) m. Using the contact angles the dispersion and non-dispersion or Lifshitz-van-der-Waals and acid base components of the surface free energy of cassiterite covered with a mixed film of SDS and TX-100 were evaluated. These components were compared to those for a "bare" cassiterite surface. Also, the electron-acceptor and electron-donor parts of the acid-base components were determined. On the basis of the measurements and calculations synergetic effects were found in the wettability and surface free energy of cassiterite when it was covered with the mixed film.