The objective of this study was to improve the flavor of Cheonggukjang prepared by the culture optimization of starter with the fibrinolytic activity. After 25 strains isolated from the commercial Cheonggukjang and Doenjang in different regions were compared, 7 Bacillus strains with proteolytic and slime-producing activities were selected. When the fibrin plate method for fibrinolytic activity was applied, CJJN-4 and 5 showed the higher activity in tripticase soy broth (TSB). All Cheonggukjang prepared with CJJN-4 and 5 also had the fibrinolytic activity, regardless of culture temperature or time. Especially, Cheonggukjang prepared at $40^{circ}C$ showed higher activity than $45^{circ}C$, and Cheonggukjang prepared with CJJN-4 for 48 hr at $40^{circ}C$ showed the highest fibrinolytic activity. Although there was no significant difference in pH of Cheonggukjang prepared with CJJN-4 or 5 during 72 hr at $40^{circ}C$, Cheonggukjang prepared with CJJN-4 at $45^{circ}C$ had lower pH until 60 hr than $40^{circ}C$ or CJJN-5. The total amino type nitrogen contents of Cheonggukjang were 1,139.6 (CJJN-4) and 1,027.6 mg% (CJJN-5) for 72 hr at $40^{circ}C$, and their producing rates were also higher at $40^{circ}C$ fermentation than $45^{circ}C$. Meanwhile, the contents of ammonia type nitrogen induced unpleasant flavor were lower in Cheonggukjang with CJJN-4 and 5 at $40^{circ}C$ than CJJN-5 at $45^{circ}C$. Therefore, Cheonggukjang fermented with CJJN-4 starter at $40^{circ}C$ had the improved flavor, such as change of amino or ammonia type nitrogen production, and higher fibrinolytic activity.