We developed a secure medical image transmission system by using TCP2 which is a new technology that establishes secure communications in transport layer. Two experiments were conducted; TCP2 performance tests, and field tests that transmit real-time digital video image in domestic and international settings by equipping TCP2 with DVTS (Digital Video Transmission System). The results showed DVTS equipped with TCP2 has enough performance to send secure and high quality medical images. It was considered that medical network using TCP2 would contribute as an essential technology to telemedicine.