The present invention provides a rocuronium formulation having excellent stability. This formulation includes rocuronium and a buffer solution, and has a pH adjusted to 3.5 or less (for example, 2.5-3.5). 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. This type of rocuronium formulation has a rocuronium analog C generation rate of 5% or less after being stored for six months at 40 °C, for example.
