Provided is a sterilization method capable of performing a sterilization treatment with high sterilization efficiency using ozone produced from an air regardless of the humidity of the air as an ozone raw material gas. In the sterilization method, the air as an ozone raw material gas is irradiated with light for producing ozone which does not include light with a wavelength region where the light decomposes ozone and which has a wavelength of not more than 200 nm to obtain an ozone-containing air, and an object to be sterilized is exposed to the ozone-containing air to sterilize the object. In the sterilization method, the relative humidity of the ozone raw material gas is not more than 60% RH.