Altered　cerebral　gray　matter　volume　(GMV)　is　commonly　found　in　patients　with　chronic　pain.　Chronic　pain　is　the　prominent　characteristic　of　knee　osteoarthritis　(KOA),　yet　little　is　known　about　its　morphological　changes　in　the　brain.　Here　an　MRI　study　was　performed　to　examine　the　structural　brain　abnormalities　in　30　KOA　patients　with　knee　pain　and　age-matched　healthy　subjects.　We　detected　that　the　patients　exhibited　significant　almost　2-fold　age-related　decreases　of　GMV　compared　to　healthy　controls.　Moreover,　KOA　patients　also　had　significant　loss　of　regional　GMV　including　in　the　bilateral　orbital　frontal　cortex　(OFC),　the　right　lateral　prefrontal　cortex　(lPFC),　and　precentral　and　postcentral　cortices.　In　addition,　a　high　proportion　of　KOA　patients　exerted　abnormal　scores　of　Hamilton　Depression　Rating　Scale　(HAMD),　Hamilton　Anxiety　Scale　(HAMA),　Mini　Mental　State　examination　(MMSE),　and　Montreal　Cognitive　Assessment　(MoCA)　compare　to　controls.　Our　results　imply　that　chronic　pain　conditions　which　preferentially　involve　PFC　might　consider　as　a　＂cognitive　state.＂　And　emotion　and　cognitive　function　about　chronic　pain　should　be　highly　regarded.