Overproduction of L-ornithine by mutant strains isolated from Brevibacterium detoglutamicum BK1046 was investigated. The strain was a L-ornithine auxotroph and exhibited culture instability during fermentation. Through a sequential screening effort, a highly stable strain with lless revertant formation was finally selected and designated B. ketoglutamicum BK52 (KCTC0141BP). It prouduced L-ornithine at a high concentration (above 9 g/L) independent of subculture or cultivation time, and also had a very low tendency of revertant formation. In a long-term storage, this strain maintained its cell stability and productivity of L-ornithine to a reasonable range.