A novel fibrinolytic enzyme is isolated from one species of Pheretima by means of homogenizing, extracting with an extractive agent, precipitating with ammunonium sulfate, ultrafiltration and chromatography. The enzyme consists of a single chain with an M. W. of 22,000. It can not only dissolve human thrombi and fibrin directly and strongly, but also activate human plasminogen. The enzyme shows little toxic and side effects in animal tests. The activity, purity and etraction-rate of the enzyme in this report are all very high.