The temperature dependence of the refractive index of SrTiO3, near room temperature, has been found to be −5.1×10−5 °C−1at 632.8 nm by a variation of the minimum deviation prism method. We found that this temperature dependence had to be included to account correctly for the observed temperature sensitivity of coupling light to lithium niobate optical waveguides with strontium titanate prisms.