EEG　(electroencephalography),　as　a　noninvasive　and　inexpensive　method,　is　widely　used　to　measure　brain　function　and　make　inferences　about　regional　brain　activity.　The　stationarity　of　EEG　has　been　investigated　by　many　researchers,　while　the　stationarity　of　EEG　segment　with　ERPs　(Event-related　Potentials)　has　hardly　been　concerned　about.　It　is　necessary　to　analyze　the　stationarity　of　this　kind　of　EEG.　In　this　paper,　we　concentrate　on　the　stationarity　of　the　EEG　with　ERPs　by　testing　the　stationarity　of　500ms　EEG　segments　with　ERPs　recorded　from　six　subjects　in　two　types　of　experiments.　The　results　suggest　that　selected　EEG　segment　whose　length　is　larger　than　190ms　remains　to　be　stationarity　and　all　epochs　duration　less　than　40ms　is　considered　to　be　stationary,　whichever　channel　the　data　is　from　and　whatever　type　of　cognitive　task　is　performed　in　the　experiment.　This　is　an　obvious　difference　between　the　stationarity　of　EEG　with　ERPs　and　that　of　EEG,　which　is　reported　to　be　stationary　as　long　as　its　length　is　less　than　12s.　©　(2012)　Trans　Tech　Publications,　Switzerland.