Hydroxyl release of red soil and latosol surfaces was quantitatively measured using a self-made constant pH automated titration instrument, to study the changes of hydroxyl release with different added selenite amounts and pH levels, and to study the effects of electrolytes on hydroxyl release. Hydroxyl release increased with the selenite concentration, with a rapid increase at a low selenite concentration while slowing down at a high concentration. The pH where maximum of hydroxyl release appeared was not constant, shifting to a lower valus with increasing selenite concentration. Hydroxyl release decreased with increasing electrolyte concentration, and the decrease was very rapid at a low electrolyte concentration but slow at a high electrolyte concentration. For NaClO4, NaCl and Na2SO4 hydroxyl release was in the order of NaClO4 > NaCl 》 Na2SO4, and the difference was very significant. But for NaCl, KC1 and CaCl2, the order of hydroxyl release was NaCl > KC1 > CaCl2, and the difference was smaller. T Hydroxyl release of red soil and latosol surfaces was quantitatively measured using a self-made constant pH automated titration instrument, to study the changes of hydroxyl release with different added selenite amounts and pH levels, and to study the effects of electrolytes on hydroxyl release. Hydroxyl release increased with the selenite concentration, with a rapid increase at a low selenite concentration while slowing down at a high concentration. The pH where maximum of hydroxyl release had been constant, shifting to a lower valus with increasing selenite concentration. Hydroxyl release decreased with increasing electrolyte concentration, and the decrease was very rapid at a low electrolyte concentration but slow at a high electrolyte concentration. For NaClO4, NaCl and Na2SO4 hydroxyl release was in the order of NaClO4> NaCl "Na2SO4, and the difference was very significant. But for NaCl, KCl and CaCl2, the order of hydroxyl release was NaCl> KCl> CaCl2, and the differ ence was smaller. T