In this research, Rapeseed dregs (RDs), as a byproduct of agriculture (derived from processing of rapeseed for oil production), were originally employed as a new carbonaceous precursor to synthesize hierarchically porous and heteroatom-doped activated carbons (ACs) with the activation of ZnCl2 at various high temperatures. A variety of measurements have been adopted to systemically characterize the RD-derived ACs. The micro-morphology, pore structures and surface chemistry property were fully investigated by SEM, TEM, XRD, Raman, N-2 adsorption-desorption analysis, XPS and IR, respectively. The RD-derived ACs possess as large specific surface area as up to 1416.966 m(2) g(-1) and the pore size distribution concentrates on 1-2, 2-5, 5-15 and 25-35 nm, indicating their hierarchically porous structures. Furthermore, electrochemical measurements including electrochemical impedance spectroscopy (EIS), galvanostatic charge/discharge (GCD) and cyclic voltammetry (CV) were conducted to estimate RDAC's supercapacitive performance and rate capability. The investigations illustrated that RD derived ACs reached as high specific capacitance as 170.5 and 153.2 F g(-1) at a scan rate of 5 mV s(-1) in 1 M H2SO4 and 1 M Et4NBF4/AN, respectively. In addition, the RD-derived ACs demonstrated good long-term cycling stability and more than 90% initial capacity have been retained after 6400 cycles at a large current density of 1 A g(-1).