Aeration device for bioreactors with an aeration element with gas outlet openings arranged in a housing, the aeration element taking the form of a microsparger, the gas outlet openings of which are in each case spaced apart from one another and have a size of between 100 μm and 200 μm. At least one second aeration element with gas outlet openings of a second size is preferably provided, the aeration elements being formed by a common housing with separate aeration channels.