To provide a stable water-based medicinal composition comprising allantoin. Provided are a water-based medicinal composition, said composition comprising allantoin and hydrogen chloride, etc. The water-based medicinal composition according to the present invention, in which allantoin remains stable even at a high pH value, is useful in eye washes, etc.本發明以提供搭配尿囊素且安定的水性醫藥組成物為課題。本發明提供含有尿囊素以及氯化氫之水性醫藥組成物等。本發明之水性醫藥組成物為,即使在高pH下尿囊素仍然穩定,對洗眼劑等也有用。