The surface of Poly(sulfone) (PSU) and Polyurethane (PU) films were treated with ultraviolet (UV) light in the presence of oxygen to improve their wettability, adhesion and cell spreading properties. XPS and WCA results illustrated the effective conversion of the PSU and PU surfaces from hydrophobic to hydrophilic with grafting of new oxidized functional groups during the photochemical treatments. Treated films showed a larger number of adhered cells compared to the untreated films and that number of adhered cells was comparable to the number of adhered cells in the control group. The results showed that the cell response does not only depend on the hydrophilicity but on the chemical surface alterations which occur as a result of UV-assisted treatment in the presence of oxygen. Better cell adhesion, spreading and growing on the PSU and PU substrates modified by the present UV methodology confirmed the biocompatibility of the treated surfaces.