Temperature dependent emission spectra and decay times of trivalent dysprosium (${\mathrm{Dy}}^{3+}$) activated ${\mathrm{Y}}_4{\mathrm{Al}}_2{\mathrm{O}}_9$ (YAM) crystals have been studied for the first time (to our knowledge). The ratio of emission lines intensity can be used in temperature measurements, as it is not dependent on the variability of absolute intensity. The Boltzmann model was applied for modeling the temperature variation of the ${{}^4\mathrm{I}}_{15/2}$ and ${{}^4\mathrm{F}}_{9/2}$ states emissions relative intensities 455 and 481 nm, respectively. The calculated approximation gives highest sensor sensitivity of about $3\times {10}^{-3}°{\mathrm{C}}^{-1}$ for the 600°C–800°C range, which allows for an expectation of usefulness of ${\mathrm{Dy}}^{3+}\text{:}\mathrm{YAM}$ in high-temperature luminescence thermometry. Also, the measured decay times are suitable for temperature sensing.