Abstract: The Boltzmann constant kB is used in the new definition of temperature unit-Kelvin.In this article,the fluorescent spectroscopic method is introduced to determine this constant.Population of electrons in thermal coupled levels of phosphors can be described with the Boltzmann distribution.Based on temperature dependent photoluminescence of a phosphor,the Boltzmann constant is derived from the relationship between measured relative intensity and temperature.Relationship between kB and hc（the Planck constant multiplying light speed in vacuum） is derived from experimental measurement.The determined Boltzmann constant shows ～0.2% divergence upon the value recommended by CODATA in the year 2006.

Key words: Boltzmann constant, temperature, fundamental unit