We isolated a bacterial strain with the highest protease activity from Korean traditional doenjang. From the analysis of the gene sequence of 16S rRNA, the isolated strain TSD was identified as Bacillus subtilis and was therefore named B. subtilis TSD. This strain showed maximal growth and the highest protease activity after 16 h at 37°C. The protease activity of B. subtilis TSD was stably maintained at a high level in the pH range of 5∼9 but gradually decreased with increasing sodium chloride (NaCl) concentration. Starter doenjang was prepared using B. subtilis TSD, and its quality and functional properties were compared with those of the control doenjang (without starter) after 30 days of fermentation. The content of amino-type nitrogen, a quality index of doenjang, was 278 mg% in the starter doenjang, which is more than 217 mg% seen in the control doenjang. The DPPH and ABTS radical scavenging and angiotensin-converting enzyme (ACE) inhibition activities of starter doenjang were higher than those of control doenjang.