Second harmonic signals have been successfully generated for thermally poled glasses with 85%TeO2- 15%WO3 molar composition. Thermal poling was undertaken at various temperatures and heating times (voltage: 4.5 kV, sample thickness: 500 lm). The second harmonic generation (SHG) of the poled glasses was analysed using the Maker fringes technique. After optimisation of the poling conditions (T = 280 C, t = 1 h, 2 h), high v(2) values, up to 1.5 pm/V, were obtained. It was demonstrated that thermal poling has generated optically nonlinear zones at the anode side. The thickness of the SHG active layer was thin, lower than 20 lm. Two complementary hypothesis have been proposed to explain the origin of the second- order nonlinearity property of this tellurite glass: (i) a reorientation of the TeO4 glass structural entities under electric field and (ii) the formation of an anodic depletion region of sodium ions.