Resistive random-access memory (RRAM) has been widely considered for its prospective applicability owing to its non-volatile characteristics. In this study, a polymer-based vacuum-free RRAM device fabricated with the conductive polymer, poly(3,4-ethylene-dioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was proposed. Pristine PEDOT:PSS coated on indium tin oxide (ITO) electrode was used as the active layer, while PEDOT:PSS with 16 vol% ethylene glycol was added for the top electrode. The PEDOT:PSS-based RRAM device demonstrated controlled non-volatile bipolar switching and a good ON/OFF ratio with a negative differential resistance effect in the high-voltage range during the RESET process. Multi-level switching was also accomplished by controlling the voltage, which demonstrated reliable and non-volatile switching. The switching mechanism of this polymer RRAM device can be explained through the electrochemical filamentary formation as well as the current-induced phase segregation of PEDOT:PSS near the anode(ITO)/polymer interface. (https://doi.org/10.1016/j.orgel.2021.106228)