Single　Sign-On　(SSO)　is　an　important　cryptography　mechanism　in　distributed　systems.　Quantum　cryptography　has　gained　great　successes　and　makes　great　influence　on　traditional　cryptography.　In　this　paper,　a　SSO　protocol　based　on　two-state　entanglement　is　designed.　Through　security　analysis,　we　show　that　this　protocol　has　good　security　properties.