The present invention provides a method for conveniently producing a protein formulation with viruses being inactivated, without impairing the quality of the obtained protein formulation, characterized by including the step of exposing the protein formulation contaminated with the viruses to a 0.1-2M aqueous solution of arginine, an arginine derivative or a mixture thereof, the aqueous solution being adjusted to pH 3.5 to 5. The present invention also provides a virus inactivation method characterized by including the step of bringing a virus-containing object into contact with a 0.1-2M aqueous solution of arginine, a arginine derivative or a mixture thereof, the aqueous solution being adjusted to pH 3.5 to 5.
