Tissue　factor　(TF),　the　cell　surface　receptor　and　requisite　cofactor　for　the　inactive　serine　protease　factor　VIIa　(VIIa),　binds　VIIa　and　its　zymogen　factor　VII　with　picomolar　affinity　on　the　cell　surface.　The　TF:VIIa　complex　proteolytically　converts　downstream　zymogen　factors　X　and　IX　to　their　active　protease　states　in　the　cascade　responsible　for　thrombogenesis　and　hemostasis.　The　TF　pathway　also　produces　cellular　signaling　through　protease　activated　receptors.　Here　we　present　a　crystal　structure　of　the　completely　intact　surface　domain　of　TF　in　complex　with　VIIa　that　reveals　a　significant　conformational　difference　as　compared　to　free　TF.　A　long　loop　of　residue　78∼91of　the　tissue　factor　(named　Ω　loop　here)　was　found　to　have　well-ordered　conformation,　whereas　this　loop　in　free　TF　has　an　expanded　conformation　and　is　largely　disordered.　This　loop　adopts　a　tight　conformation　consisting　of　five　β　turns　in　the　TF:VIIa　complex.　The　Ω　loop　is　located　at　the　interface　of　the　proteins　of　the　complex,　has　a　few　interactions　with　VIIa,　and　is　possible　to　accommodate　the　sequence　variations　of　TF　in　different　mammalian　species.　©　2018　Fujian　Institute　of　Research　of　the　Structure　of　Matter.　All　rights　reserved.