Mode-mismatched Thermal Lens (TL) measurements were performed in 70TeO(2)-19WO(3)-7Na(2)O-4Nb(2)O(5) (% mol) tellurite glasses doped with either Er3+ or Tm3+ and co-doped with Er3+/Tm3+ ions. Thermo-optical parameters (D, K, ds/dQ and ds/dT) were obtained in function of thulium concentrations (0.39-1.6) x 10 20 ions/cm(3). For Er3+/Tm3+ co-doped tellurite glasses, D and K values are practically independent of the Tm3+ concentrations used in this study. The average values of D and ds/dT obtained for tellurite glasses are: (3.1 +/- 0.2) x 10(-3) supercript stopcm(2)/s and (16 +/- 3) x 10(-6) stopK(-1), respectively.