Disclosed is a technique for preventing the decomposition of latanoprost (a thermally unstable substance) contained in an eye-drop solution to stabilize the eye-drop solution. Specifically disclosed is an eye-drop preparation comprising latanoprost and carteolol hydrochloride. By adding carteolol hydrochloride to an eye-drop solution containing latanoprost which is a thermally unstable substance and is likely to be adhered on the surface of a container, it becomes possible to prevent the decomposition of latanoprost in the eye-drop solution and also prevent the loss of latanoprost caused by the adsorption of latanoprost on the surface of a container.
