A novel potent protease, Urechis unicinctus fibrinolytic enzyme (UFE), was first discovered by our laboratory. In this study, we further investigated the enzymatic properties and dynamic parameters of UFE. As a low molecular weight protein, UFE appeared to be very stable to heat and pH. When the temperature was < 50 degrees C, the remnant enzyme activity remained almost unchanged, but when the temperature was raised to 60 degrees C the remnant enzyme activity began to decrease rapidly. UFE was quite stable in a pH range of 3.0-12.0, especially at slightly alkaline pH values. Mn (2+), Cu2+, and Fe (2+) ions were activators of UFE, whereas Fe3+ and Ag+ ions were inhibitors. Fe (2+) ion along with Fe3+ ion might regulate UFE activity in vivo. The optimum pH and temperature of UFE were about 8.0 and 50 degrees C, respectively. When using casein as substrate and a substrate concentration < 0.1% casein (w/v), the reaction velocity was increased with substrate concentration. Also when using casein as substrate, the determined KM and V-max of UFE were 0.5298 mg/mL and 3.0845 Mol of L-tyrosine equivalent, respectively. Our systematic research results are significant when UFE is applied for medical and industrial purposes.