Passive Q switching of a flashlamp‐pumped alexandrite laser with a Cr4+:Y2SiO5 (Cr4+:YSO) solid‐state saturable absorber has been demonstrated at room temperature. An output of a single Q‐switched laser pulse of 20 mJ in energy and 70 ns in duration was obtained. The output wavelength of the Q‐switched laser pulse and the free‐running laser was 753 nm.