Deposition by adsorption of single walled carbon nanotubes (SWCNTs) onto electrodeposited poly[3,4-ethylenedioxythiophene] (PEDOT) films is reported. Electrochemical quartz crystal microbalance (EQCM) measurements in dispersive mode reveal resonance frequency decrease as well as growth of acoustic resistance during the SWCNT deposition. These data were interpreted in terms of increasing of the roughness of the surface and the corresponding change of surface impedance. The thus in situ obtained estimates of size and irregularities agree with ex situ scanning electron microscopy data. Transmission electron microscopy was used to analyze the size and the morphology of the SWCNTs, which were mostly occurring as bundles of nanotubes rather than individual ones. Electroactivity of PEDOT and PEDOT-SWCNT films was studied with regard to the detection of dopamine.