Background; FKHRL1 (forkhead transcription factor in rhabdomyosarcoma like-1) is reported to upregulate p27 and to arrest cell cycle in various cancer cell lines. Our previous study demonstrates that FKHRL1 induces apoptosis of HUVEC by inhibiting heat shock protein 70 (HSP70) expression which is an important survival factor under stress. Aim; We tested whether FKHRL1 could inhibit neointimal hyperplasia by suppression of HSP 70 and induction of P27 in balloon injury model. Method; [1] In vitro study: Adenovirus expressing the constitutively-active FKHRL1 (FKHRL1-TM; triple mutant) with three Akt phosphorylation sites mutated, was transfected to subconfluent VSMC. The effect of FKHRL1 on the expression of HSP70, P27 expression, and cell viability, was examined. [2] In vivo study: The common carotid artery of SD rat (17wks, N=15 each group) was denuded by 2 Fr Fogarty catheter. Adenoviral vectors (3 X 108 pfu of Adv-FKHRL1-TM vs GFP) were delivered to denuded segment. Animals were sacrificed 3 or 14 days after gene transfer. Result; Overexpression of FKHRL1-TM gene in cultured VSMC increased p27 and decreased HSP70 expression in immunoblot analysis which led to significant decrease of viable cell number in MTT assay. At 3 days after carotid injury, the expression of HSP70 increased, whereas p27 expression decreased in immunoblot analysis. These changes were reversed by FKHRL1-TM gene transfer, which led to the increased apoptosis of medial SMC in TUNEL assay and IHC for activated caspase-3. Histological analysis of 14 days��� sample revealed that the intima/medial ratio was reduced by 73 % in the Ad-FKHRL1-TM group compared to Ad-GFP group (0.31짹0.13 vs 1.17짹0.28, P<0.001). Conclusion; Adenovirus-mediated gene transfer of the constitutively-active FKHRL1 gene significantly inhibited neointimal hyperplasia, which was mediated by inhibition of HSP70, induction of p27, and enhanced apoptosis of VSMC after balloon injury.