Ti-6Al-4V shows distinct active-passive behaviour in phosphoric acid over a wide concentration range. The cathodic polarization curves are similar over a wide range of acid concentration and temperatures. The alloy undergoes active dissolution and turns passive in the negative potential region followed by a wide range of passivity at all acid concentrations at different temperatures. Increasing acid concentration up to 11 M results in an increase in critical current density (i(cr)). The passive current density (i(p)) increases up to an acid concentration of 9 M while at 13 M i(cr) and i(p) decrease appreciably. A significant increase in both i(cr) and i(p) occurs with increase in solution temperature. The passive specimen remained stable for a long time when exposed to phosphoric acid under open circuit conditions.