A medical device made of an ester resin, such as a hollow-fiber-type blood treatment device, is put into a packaging material made of a gas-impermeable material, and, with at least a reducing gas, such as hydrogen gas, being further enclosed therein, the packaging material is hermetically sealed to provide a medical device package. The medical device package is exposed to radiation to sterilize the inside thereof. In the medical device package, an oxygen scavenger may be further enclosed. The reducing gas may be mixed with an inert gas and enclosed as a mixed gas. As a result, it becomes possible to effectively suppress the generation of by-products, such as acetic acid, from the ester resin.
