PURPOSE: To provide a method for manufacturing a membrane type artificial lung which can prevent the deterioration of the base material by ozone at minimum and give anti-thrombotic property.

CONSTITUTION: A liquid is brought into contact with a surface making no contact with blood of either the inner surface or outer surface of a gas exchange membrane integrated into an artificial lung, whereby the pare of the gas exchange membrane is closed, and ozone is passed into the artificial lung in this state to oxidize and decompose only the surface making contact with the blood by ozone. In such a membrane type artificial lung deterioration of the whole membrane can be suppressed at minimum, and anti-thrombotic property can be given to the surface making contact with the blood.