The present invention provides a rocuronium preparation with an excellent stability. The rocuronium preparation contains rocuronium and a buffer solution and having an adjusted pH of 3.5 or less (for example, 2.5 to 3.5). The buffer solution may be a citric acid-sodium hydroxide buffer solution, a tartaric acid-sodium hydroxide buffer solution, a potassium hydrogen phthalate-hydrochloric acid buffer solution, a glycine-hydrochloric acid buffer solution, or the like. Such a rocuronium preparation has, for example, after 6-month storage at 40°C, a generation rate of rocuronium-related substance C of 5% or less.
