This work investigates the influence of transition metals oxides (Ta2O5 and ZrO2) on the nonlinear refraction of niobium-borotellurite glasses prepared by melt-quenching technique. The closed-aperture Z-scan technique was used to measure the nonlinear refractive index (n2) spectrum from 470???nm to 800???nm. Also, the BGO (Boling, Glass, and Owyoung) approach was used to model nonlinear spectra, considering the oxygens present in the sample as the major contribution to the nonlinearity. The samples??? molar electronic polarizability was determined to further understanding the effect of the transition metals oxides on the optical properties. Structural analysis was performed by differential scanning calorimetry, Raman and Infrared spectroscopies. The results indicate that although the modifier oxides affect the structural units and glass polarizability, they are not enough to change the behavior of the nonlinear refractive index spectra, being the glass-matrix the main responsible for optical nonlinearity in the system studied here.Coordena????o de Aperfei??oamento de Pessoal de N??vel Superior (CAPES)Funda????o de Amparo ?? Pesquisa do Estado de S??o Paulo (FAPESP)CAPES: 001FAPESP: 18/11283-7