In　order　for　practical　applications　in　vacuum　electron　devices,　the　robustness　of　scandia-doped　dispenser　(SDD)　cathode　is　a　major　concern.　Emission　properties　after　air　exposure　and　gas　poisoning　have,　therefore,　been　studied.　A　full　restoring　of　emission　has　been　proved　after　the　cathodes　were　exposed　to　air　and　reactivated　for　a　time　much　shorter　than　initial　activation.　Poisoning　experiments　demonstrated　that　the　poisoning　pressure　thresholds　of　residual　gases　for　the　SDD　cathode　are　about　half　to　one　order　of　magnitude　higher　at　equivalent　temperatures　but　with　higher　emission　level　in　comparison　with　that　of　an　excellent　M　cathode.　The　cathode　is　easier　to　recover　after　poisoning　and　can　operate　stably　in　a　nonideal　environment.　These　features　are　thought　to　be　related　to　the　surface　Ba-Sc-O　structure　which　has　closely　chemical　association,　better　stability　for　air　exposure,　relatively　high　tolerance　to　gas　poisoning,　and　the　semiconductor　emission　characteristic.