The effect of a plasma treatment on polymers is not permanent, since the treated surfaces tend to recover to the untreated state (ageing process). This paper investigates the influence of discharge atmosphere on the ageing behaviour of plasma-treated PLA foils: these foils are plasma-treated with a DBD in 4 different atmospheres (air, nitrogen, argon and helium) and are subsequently stored in air. Results of contact angle and XPS measurements show that the discharge gas has a significant influence on the ageing behaviour of the PLA foils. This influence can be explained by the different cross-linking degree of the plasma-treated surfaces: helium and argon plasma-treated PLA films have a high cross-linking degree, which limits polymer chain mobility and as a result reduces the ageing process. In contrast, the ageing behaviour of air and nitrogen plasma-treated films is more pronounced due to their low cross-linking degree.