Purpose: The purpose of this study is to compare the efficacy and safety of 2% long-acting carteolol solution with 0.5% timolol gel-forming solution added to primary treatment of 0.005% latanoprost solution in patients with primary open-angle glaucoma and ocular hypertension. Materials and Methods: After at least 4 weeks primary treatment with latanoprost, all patients received the combination therapy with either 2% long-acting carteolol or 0.5% timolol gel in addition to latanoprost for 8 weeks. We measured intraocular pressure (IOP) and evaluated systemic and local adverse events between Day 1 and Day 56. Results: Carteolol significantly reduced the IOP from baseline (latanoprost monotherapy) by 11.0% at Day 28 and 11.2% at Day 56. Timolol also reduced IOP by 11.5% at Day 28 and 11.0% at Day 56. There was no statistically significant difference in the IOP reduction between the two groups. There was no adverse event related to the administration of these anti-glaucoma medications during the study period. Conclusions: Both once daily carteolol and timolol medications are safe and effective treatments combined with latanoprost single therapy.