The influence of atmospheric carbonation on gas diffusion was investigated using four hardened cement pastes (CEM I, CEM III-A, CEM V-A and a low-alkalinity binder) with common water-to-binder ratio (0.4). The diffusivity to helium and nitrogen of the non-carbonated and carbonated pastes was measured at different relative humidities. Carbonation decreased the diffusivity of the CEM I paste whereas that of the other binders significantly increased after carbonation. These results show the competition between porosity clogging and cracking induced by carbonation. The consequence of carbonation are then believed to depend on the considered binder. For OPC, clogging dominates leading to the decrease in transport properties after carbonation whereas cracking dominates for blended cements leading to significant increase in transport properties after carbonation.