TheR‐line fluorescence in ruby was excited with the nanosecond light pulses, and the slope of the rise curve was studied as a function of the pulse width at room temperature. The purpose of the experiment was to determine the value or the upper limit of the nonradiative relaxation time between the pump bands4T1, 2and the fluorescence state2E. The upper limit of 5 nsec was determined. A brief review of previous work is given.