As‐grown single‐crystal ruby fibers have been operated continuously as end‐pumped lasers, in air at room temperature, without active cooling. The fiber laser elements were about 40 &mgr;m in diameter and 0.25 cm long, with a Cr3+concentration of 0.02&percent;. The pump source was a Kr laser. Continuous operation was in a single transverse mode at one to five longitudinal resonant frequencies, the observed relaxation oscillations were regular and periodic, and the output was plane polarized. Fiber growth is described, and both transient and steady‐state heating effects in the laser due to pump absorption are discussed.