The thermo-optic coefficients of single phase pure and Ni doped ZnO thin films are calculated from the experimentally obtained values of their nonlinear refractive indices using Z-scan technique. The optical nonlinearity as obtained by using a cw He-Ne laser is assigned to the thermal lensing effect. The positive and negative values of the thermo-optic coefficients of the films suggest that ZnO/NiZnO/ZnO combination can form athermal wave-guide structure which can be useful in making thermally stable optoelectronic devices. (C) 2016 Elsevier B.V. All rights reserved.