Abstract: The extraction of antibacterial protamine from carp spermary by ultrasonic technology was studied. The results show that H₂SO₄ concentration is low, and extracting time is also short by using ultrasonic technology. Protamine of higher antibacterial activity could be extracted with 1.0 A ultrasound, 5% H₂SO₄ for 20 min. And the effects of pH values, temperature, metal ion, protease on protamine antibacterial activity were also investigated.