This paper describes metallization of PET surface by Sn-free electroless deposition (ELD) of thin copper layer. Prior to introduction to ELD process, the PET surface was plasma-pretreated in argon atmosphere. ELD is a multi-step process involving silanization with TMS, activation with PdCl2 and copper deposition. Contact angle measurement and XPS analysis were carried out at each stage in order to confirm the chemical change of the PET surface after modification. XPS analysis revealed that the copper surface consisted mainly of Cu2O, combined with Cu0, making Cu-coated PET sheet suitable for the use as substrate for electropolymerization of pyrrole. This study offers an alternative to preparing flexible sensors. This process could be further applied to micro-contact printing technique to fabricate flexible patterned electrodes.