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,　we　combines　the　SSO　mechanism　and　quantum　cryptography　together.　A　SSO　protocol　based　on　four-state　entanglement　is　designed.　Through　security　analysis,　we　show　that　this　protocol　has　good　security　properties.