Dy3+-and Nd3+-doped YNbO4 powders were prepared using a mechanochemical method followed by annealing, and their photoluminescent properties were examined to assess the possibility of their use in phosphor thermometry. Luminescence intensity ratio technique was used as a temperature read-out scheme for both YNbO4:Dy3+ and YNbO4:Nd3+ samples. The crystalline structure of the samples is confirmed by XRD measurements, while SEM was used for the microstructural and compositional characterization. Sample doped with Dy3+ ions emitting in the blue region has been investigated in the 293–773 K temperature range and exhibits maximal relative sensitivity of 1.97% K−1 at 300 K. YNbO4:Nd3+ sample showed intense NIR emission which fall into the first biological window. When heated from 303 up to 473 K relative temperature sensitivity of 0.28% K−1 at 300 K was achieved. Values of temperature sensitivities show that YNbO4 has a large potential for the development of thermographic phosphors in the blue and NIR spectral ranges when doped with trivalent Dy and Nd, respectively.