Graft copolymers made of all-conjugated polythiophene (PTh) backbone and well-defined poly(ethylene glycol) (PEG) side chains have been prepared using different macromonomers, which differ in the number of thiophene (Th) rings. The effects of the PEG / Th ratio on both bulk and surface properties as well as in the behavior of these materials as bioactive platforms have been evaluated. Furthermore, the properties of these copolymers have been compared with those of poly(-terthiophene) (PTh3). The band gap of the PTh backbone has been found to decrease with PEG / PTh ratio. Similarly, the electrochemical properties (i.e. electroactivity and electrochemical stability) improve with decreasing PEG / Th ratio. Interestingly, both the ability to exchange charge reversibly and the electrostability of the copolymers are higher than those of PTh3, which has been attributed to the compact structure of the latter. All investigated copolymers are biocompatible materials, even though the ability to promote cell growth increases with decreasing PEG / Th ratio. In spite of this, PTh3 has been found to be cytotoxic due to the release of medium size compounds from the polymeric matrix to the culture medium. In order to eliminate the cytotoxicity of PTh3, a strategy based on the deposition of a thin layer of collagen has been proposed. Finally, graft copolymers coated with cells behave as electro-compatible materials. Thus, the electrochemical activity and the maximum of current density are remarkably higher for samples coated with cells than for uncoated samples. This effect increases with decreasing PEG / Th ratio. The excellent properties of copolymers made of PTh with grafted PEG chains suggest that these materials can be used as bioactive platforms for multiple biotechnological and biomedical applications in which the transmission with cells is carried out at the electrochemical level.