The　urokinase-type　plasminogen　activator　receptor　(uPAR)　is　a　cell　surface　receptor　that　is　capable　of　binding　to　a　range　of　extracellular　proteins　and　triggering　a　series　of　proteolytic　and　signaling　events.　Previous　structural　studies　of　uPAR　with　its　ligands　uPA　and　vitronectin　revealed　that　its　three　domains　(DI,　DII,　and　DIII)　form　a　large　hydrophobic　cavity　to　accommodate　uPA.　In　the　present　study,　the　structure　of　unoccupied　murine　uPAR　(muPAR)　is　determined.　The　structure　of　DII　and　DIII　of　muPAR　is　well　defined　and　forms　a　compact　globular　unit,　while　DI　could　not　be　traced.　Molecular　dynamic　simulations　further　confirm　the　rigid　binding　interface　between　DII　and　DIII.　This　study　shows　overall　structural　flexibility　of　uPAR　in　the　absence　of　uPA.