Abstract: Non-repudiation is one of the most important premises to achieve electronic commerce. Based on a trusty third party, this paper proposes a transmission-oriented electronic evidence and non-repudiation protocol transmission-oriented electronic evidence and non-repudiation protocol (TEENP) to resolve the possible repudiation problem both in receiver side and in sender side. We extend the semantics and reasoning rules of the belief logic BAN, and formal analysis of TEENP is presented using logic BAN. The protocol is fair, secure and efficient, compared with the corresponding protocols.