Sensor　networks　are　widely　used　in　a　variety　of　commercial　and　military　applications　due　to　their　self-organization　characteristics　and　distributed　nature.　As　a　basic　requirement　for　supporting　security　in　sensor　networks,　key　management　plays　an　essential　role　in　authentication　and　encryption.　In　this　paper,　we　describe　the　hexagon-based　key　predistribution　scheme　and　show　that　it　can　improve　the　effectiveness　of　key　management　in　sensor　networks.　We　show　that　this　key　management　scheme　can　improve　the　probability　of　establishing　pairwise　keys　between　sensor　nodes　of　up　to　two　hops　apart　by　more　than　40%　over　other　schemes.　We　also　show　that　the　security　of　a　sensor　network　would　decrease　with　the　increase　in　sensor　node　deployment　density　or　in　signal　propagation　distance.　©　Springer-Verlag　Berlin　Heidelberg　2006.