Flexible supercapacitor plays a progressively more important part in power source for smart electronic devices and how to enhance its energy density is the urgent issue to be addressed. Hence, a hybrid electrode of Polypyrrole@reduced graphene oxide hydrogel (PPy@rGOH) is synthesized via a combine hydrothermal treatment of GO solution to assemble hydrogel and subsequently in-situ electropolymerization preparation of PPy on the surface of graphene. Through controlling the time of electropolymerization, the resultant PPy@rGOH-20 s with high specific surface area exhibits an excellent specific capacitance of 340 F g(-1) at a current density of 1 A g(-1) and superior cycling stability of 87.4% capacitance retention after 10,000 charging/discharging cycles at 3 A g(-1) in 1 M KNO3. The assembled flexible asymmetric supercapacitor (FASC) by employing the PPy@rGOH-20s as positive electrode and pure rGOH as negative electrode presents a maximum operational voltage window of 1.6 V and high energy density of 46.9 W h kg(-1), which is higher than polymer/carbon-based supercapacitors previously reported. (C) 2018 Elsevier Inc. All rights reserved.