Previous　studies　of　young　people　have　revealed　that　the　left　dorsolateral　prefrontal　cortex　(DLPFC)　plays　an　important　role　in　inductive　reasoning.　An　fMRI　experiment　was　performed　in　this　study　to　examine　whether　the　left　DLPFC　was　involved　in　inductive　reasoning　of　MCI　patients　and　normal　agings,　and　whether　the　activation　pattern　of　this　region　was　different　between　MCI　patients　and　normal　agings.　The　fMRI　results　indicated　that　MCI　patients　had　no　difference　from　normal　agings　in　behavior　performance　(reaction　time　and　accuracy)　and　the　activation　pattern　of　DLPFC.　However,　the　BOLD　response　of　the　DLPFC　region　for　MCI　patients　was　weaker　than　that　for　normal　agings,　and　the　functional　connectivity　between　the　bilateral　DLPFC　regions　for　MCI　patients　was　significantly　higher　than　for　normal　agings.　Taken　together,　these　results　indicated　that　DLPFC　plays　an　important　role　in　inductive　reasoning　of　agings,　and　the　functional　abnormity　of　DLPFC　may　be　an　earlier　marker　of　MCI　before　structural　alterations.