The　microstructure　and　physical　behaviour　of　active　substance　of　scandia　mixed　tungsten　matrix　and　its　impregnated　cathode　were　studied　by　XRD,　SEM,　and　AES　methods.　The　results　show　that　Sc(2)O(3)　dispersed　evenly　in　the　matrix.　During　the　activation　period　of　the　cathode,　the　surface　active　layer　containing　Ba,　Sc　and　O　is　formed　due　to　the　simultaneous　diffusion　of　Ba,　Sc　and　O　from　the　inner　part　of　the　cathode　to　the　surface.　The　thickness　of　this　active　layer　is　more　than　ten　times　larger　than　that　of　＂M＂　type　cathode.　The　production　mechanism　of　free　scandium　was　discussed.