Nitrated and sulfonated PEEK-WC with various degrees of substitution were obtained. The modified PEEK and its derivatives are able to form asymmetric membranes. The sulfonation was carried out to increase hydrophilicity and permeability. The insertion of the nitro group allow us to obtain a new material with possible positive properties and also to have a reactive group suitable for further modifications through previous reduction to the amino group. Symmetric and asymmetric membranes made from these polymers were prepared and characterized. The influence of evaporation time, and of the functional groups on membrane morphology and performances were analyzed. Membrane morphology was investigated by using Atomic Force Microscopy.