A faucet aerator comprises: a casing and a guiding member. The casing has a water inlet 11 and a water outlet. The water inlet is provided with a threaded portion for engaging with a faucet. The casing is further provided with at least one ring groove at an inner surface for engaging with the guiding member. The guiding member has a barrel body with a pre-filter, and the pre-filter is provided with at least one ring rib for engaging with the ring groove when the guiding member is placed in the casing, to avoid the guiding member from escaping the casing while the aerator is cleaned. The barrel body provided with a plurality of through apertures, a bottom mesh, and a first aerating mesh.