<;P>;PROBLEM TO BE SOLVED: To provide a new sperm activator safe and inexpensive and good in workability as well, enabling sperm activity to be maintained even under long-term storage, and to provide a method for activating sperm. <;P>;SOLUTION: The sperm activator is characterized by that protamine is included, as protamine sulfate salt, in concentration ranging from 0.1 to 0.5 g/L in a solution after diluting semen. The method for activating sperm is characterized by comprising adding protamine, as protamine sulfate salt, to semen so that its concentration falls within the range between 0.1 and 0.5 g/L in a solution after diluting the semen. <;P>;COPYRIGHT: (C)2010,JPO&INPIT