MED1 (Mediator complex subunit 1) is a co-activator of various transcription factors that function in multiple transcriptional pathways. We have already established keratinocyte-specific MED1 null mice (Med1 epi-/-) that develop epidermal hyperplasia. Herein, to investigate the function(s) of MED1 in skin wound healing, full-thickness skin wounds were generated in Med1epi-/- and age-matched wild-type mice and the healing process was analyzed. Macroscopic wound closure and the re-epithelialization rate were accelerated in 8-week-old Med1epi-/- mice compared with age-matched wild-type mice. Increased lengths of migrating epithelial tongues and numbers of Ki67-positive cells at the wounded epidermis were observed in 8-week-old Med1epi-/- mice, whereas wound contraction and the area of α-SMA-positive myofibroblasts in the granulation tissue were unaffected. Migration was enhanced in Med1 epi-/- keratinocytes compared with wild-type keratinocytes in vitro. Immunoblotting revealed that the expression of follistatin was significantly decreased in Med1epi-/- keratinocytes. Moreover, the mitogen-activated protein kinase pathway was enhanced before and after treatment of Med1epi-/- keratinocytes with activin A in vitro . Cell-cycle analysis showed an increased ratio of S phase cells after activin A treatment of Med1epi-/- keratinocytes compared with wild-type keratinocytes. These findings indicate that the activin-follistatin system is involved in this acceleration of skin wound healing in 8-week-old Med1epi-/- mice. On the other hand, skin wound healing in 6-month-old Med1epi-/- mice was significantly delayed with decreased numbers of Ki67-positive cells at the wounded epidermis as well as BrdU-positive label retaining cells in hair follicles compared with age-matched wild-type mice. These results agree with our previous observation that hair follicle bulge stem cells are reduced in older Med1epi-/- mice, indicating a decreased contribution of hair follicle stem cells to epidermal regeneration after wounding in 6-month-old Med1 epi-/- mice. This study sheds light on the novel function of MED1 in keratinocytes and suggests a possible new therapeutic approach for skin wound healing and aging.