As is always accompanying temperature in physics fundamental principles, Boltzmann constant kB can be used to verify the accuracy of a thermometer. This paper presents a photoluminescent method to measure kB via temperature dependent fluorescence of phosphors. Diagram of a phosphor’s energy levels was simplified to illustrate the principle of measurement. The relationship between kB and h*c (Planck constant h multiplying light speed in vacuum c) was experimentally derived. Finally, the determined kB was 1.38065×10-23 J/K. The determination could give a value of (1.38±0.1)×10-23 J/K even when the in-use spectrometer was with a poor resolution as about 2 nm. At the end, optimization of measuring conditions for the determination process was suggested.