For the first time the temperature dependence of the photoluminescence of the semiconductor CsPbBr ₃ perovskite nanocrystals with sizes of 6.0–9.0 nm in fluorophosphate glass were investigated in the temperature range from 300 K to 423 K. It was shown that temperature dependence of the photoluminescence intensity and the band gap shift coefficient change at 350 K corresponding to the isostructural phase transition. The photoluminescence intensity decreased radically above this temperature. The temperature energy gap coefficients of the CsPbBr ₃ nanocrystals depending on the size and temperature range were found.