The aim of this study was to evaluate the one-year efficacy, ability to lower intraocular pressure, and tolerability of ripasudil, a rho-kinase inhibitor, in patients with glaucoma inadequately controlled with maximum medical therapy. This prospective, non-comparative, interventional case-series study included 39 patients with primary open-angle glaucoma inadequately controlled with maximum medical therapy before treatment with ripasudil. Ripasudil was administered twice per day as adjunctive therapy to ongoing glaucoma treatment. The primary endpoint was the degree of intraocular pressure reduction after 12months of treatment; the secondary endpoints were the incidence of adverse events. We examined 39 eyes. The intraocular pressure reduction (given as the relative percentage of intraocular pressure reduction) from baseline was -2.6mmHg (-15.5%; 95% confidence interval, -1.1 to -3.9mmHg; P<0.001) after 12months of treatment. The adverse events were conjunctival hyperemia (all patients), blepharitis (three), allergic conjunctivitis (two), punctate keratitis (two), and ophthalmalgia (one). Treatment with ripasudil decreased intraocular pressure in patients with glaucoma that was poorly controlled with maximal medical therapy, and it was well-tolerated.