Background:　Bone　marrow　mesenchymal　stem　cells　can　differentiate　into　renal　tubular　epithelial　cells.　It　is　speculated　that　mesenchymal　stem　cells　may　have　a　therapeutic　role　in　chronic　renal　dysfunction.　Objective:　To　study　the　effect　of　bone　marrow　mesenchymal　stem　cells　on　the　aging　kidney　of　rats　and　its　possible　mechanism.　Methods:　Aging　models　were　established　in　rats.　Rat　bone　marrow　mesechymal　stem　cells　cultured　in　vitro　were　labeled　by　5,6-carboxyfluorescein　diacetate,　succinimidyl　ester,　and　then　injected　into　the　rats　via　the　tail　vein.　Under　a　fluorescence　microscope,　the　cell　homing　was　observed.　The　contents　of　urea　nitrogen　and　creatinine　in　serum　of　rats　were　tested　by　automatic　biochemical　analyzer.　The　overlaying　of　blue　fluorescent　2-(4-amidinophenyl)-6-indolecarbamidine　dihydrochloride　and　the　specific　protein　of　red　fluorescent　tubular　epithelial　cells　(keratin　protein)　was　detected　by　indirect　immunofluorescence　and　computer　image　stacking　Results　And　Conclusion:　Bone　marrow　mesenchymal　stem　cells　could　arrive　the　kidney　of　rats.　Compared　with　the　model　group,　the　contents　of　urea　nitrogen　and　creatinine　in　serum　were　decreased　in　the　treated　group　(P　＜　0.05).　The　treated　group　showed　a　small　amount　of　double　positive　cells.　These　findings　indicate　that　rat　bone　marrow　mesenchymal　stem　cells　may　differentiate　into　renal　tubular　epithelial　cells,　which　may　be　one　of　mechanisms　that　improve　the　aging　kidney　of　rats.