The top surface of polyetherimide (PEI) flat sheet mernbranes was modified using fluorinated surface modifying macromolecule (SMM). The SMM modified and unmodified membranes were prepared by the phase inversion method from casting solutions containing the solvent N,N-dimethylacetamide and the non-solvent gamma-butyrolactone (GBL). The effect of the base polymer concentration on the membrane properties has been investigated. It was found that SMM actively migrated to the air surface and changed the surface properties of the PEI membranes. Contact angle measurements indicate that the PEI membrane surface becomes more hydrophobic after adding the SMM to the PEI casting solutions, while X-ray photoelectron spectroscopy analysis shows enrichment of fluorine on the PEI membrane surfaces. The SMM modified and unmodified PEI membranes were also characterised by means of liquid entry pressure of water measurements (LEPw) and gas permeation test using nitrogen as standard gas. SMM modified PEI membranes have potential to be used in membrane distillation.