We investigated whether atorvastatin (AT) was capable of protecting animals from acute graft-versus-host disease (aGVHD) across major histocompatibility complex (MHC) mismatch barriers. AT treatment of the donor induced a Th-2 cytokine profile in the adoptively transferred T cells and reduced their in vivo expansion, which translated into significantly reduced aGVHD lethality. Host treatment down-regulated costimulatory molecules and MHC class II expression on recipient antigen-presenting cells (APCs) and enhanced the protective statin effect, without impacting graft-versus-leukemia (GVL) activity. The AT effect was partially reversed in STAT6(-/-) donors and abrogated by L-mevalonate, indicating the relevance of STAT6 signaling and the L-mevalonate pathway for AT-mediated aGVHD protection. AT reduced prenylation levels of GTPases, abolished T-bet expression, and increased c-MAF and GATA-3 protein in vivo. Thus, AT has significant protective impact on aGVHD lethality by Th-2 polarization and inhibition of an uncontrolled Th-1 response while maintaining GVL activity, which is of great clinical relevance given the modest toxicity profile of AT.