The lifetime &tgr; of theR1fluorescence line,2E(E¯)→4A2of ruby (Al2O3:Cr3+) has been measured under high‐pressure conditions (up to 42.7 GPa) using a modulation fluorometry technique. This study shows that &tgr; increases linearly with pressure and that this increase is primarily caused by a rapid decrease in the transition probability of the radiative transition. The present measurements agree qualitatively with the theoretically predicted decrease in the oscillator strength at high pressure.