Idiopathic pulmonary fibrosis (IPF) is a progressive and typically fatal lung disease for which no effective therapy has been identified. The disease is characterized by excessive collagen deposition, possibly in response to dysregulated wound healing. Mediators normally involved in would healing induce proliferation of fibroblasts and their differentiation to myofibroblasts that actively secrete collagen. Curcumin, a polyphenolic compound from turmeric, has been shown to exert a variety of biological effects. Effects on IPF and associated cell types remain unclear, however. We accordingly tested the ability of curcumin to inhibit proliferation and differentiation to myofibroblasts by human lung fibroblasts, including those from IPF patients. To further examine the potential usefulness of curcumin in IPF, we examined its ability to reduce fibrosis in bleomycin-treated mice. We show that curcumin effectively reduces profibrotic effects in both normal and IPF fibroblasts in vitro and that this reduction is accompanied by inhibition of key steps in the transforming growth factor-β (TGF-β) signaling pathway. In vivo, oral curcumin treatment showed no effect on important measures of bleomycin-induced injury in mice, whereas intraperitoneal curcumin administration effectively inhibited inflammation and collagen deposition along with a trend toward improved survival. Intraperitoneal curcumin reduced fibrotic progression even when administered after the acute bleomycin-induced inflammation had subsided. These results encourage further research on alternative formulations and routes of administration for this potentially attractive IPF therapy.