The Rho-associated coiled-coil containing protein kinase, (Rho-kinase or ROCK) undergoes activation by oxidative stress. ROCK-II, which is an isoform of ROCK, is activated in a murine model of lung fibrosis. The present study evaluated the level of oxidative stress and activation of ROCK-II in patients with idiopathic pulmonary fibrosis (IPF). The ROCK-II level and the phosphorylation of myosin phosphatase subunit-1 (p-MYPT-1), a hallmark of ROCK activation, were examined by immunohistochemistry of lung tissue sections. The 8-iso prostaglandin-F2alpha (8-isoPGF2alpha) level, as a marker of oxidative stress, of exhaled breath condensate was significantly higher in IPF patients than in control patients. In IPF lungs, ROCK-II was predominantly expressed by bronchial epithelial cells, as well as at a lower level by airway smooth muscle cells, vascular smooth muscle cells, and the fibroblasts of fibroblastic foci (FF). In addition, there was moderate p-MYPT-1 expression in these cells of IPF lungs. In control lungs, ROCK-II was expressed by these cells. p-MYPT-1 was weakly expressed by the bronchial epithelial cells. In conclusion, ROCK-II was activated in various lung cells of IPF patients along with oxidative stress detected by 8-isoPGF2alpha elevation. The ROCK pathway may play a role in the development of IPF oxidative stress.