Wireless　sensor　networks　are　widely　used　in　a　variety　of　commercial　and　military　applications　due　to　their　self　organization　characteristics　and　distributed　nature.　As　a　fundamental　requirement　for　providing　security　functionality　in　sensor　networks,　key　management　plays　an　essential　role　in　authentication　and　encryption.　We　propose　a　group-based　dynamic　key　management　scheme　in　wireless　sensor　networks.　In　our　scheme,　there　is　no　requirement　for　such　infrastructure　as　base　stations　and　cluster　heads　in　order　to　maintain　the　generality　and　the　dynamic　key　update　feature　ensures　the　security　of　the　network　without　tampering　the　compromised　sensor　nodes.　We　also　analyze　the　connectivity　and　security　of　the　proposed　scheme.