Porous carbons with high capacitive properties derived from biomass have been increasingly studied for supercapacitor applications. In this work, we prepared N-doped porous carbon through a one-pot MgCl2 activation of lotus root flour with urea. A series of lotus root carbons with different physical/chemical properties were synthesized by adjusting precursors and pyrolysis temperatures. The MgCl2 activation could produce abundant micropores and mesoporous channels in nanocarbons, which are beneficial for ions adsorption and diffusion. The addition of urea improved the porosity, specific surface area, and N content in the carbons, which increased the double-layer capacitance and pseudo-capacitance. MgLC-142-800 with best performance was prepared from a mixture of lotus root flour, MgCl2, and urea with the proportion of 1:4:2 at 800 degrees C, exhibiting high specific capacitance (331.80 and 267.63 F g(-1) at 1 A g(-1 )in the three- and two-electrode system, respectively), excellent rate capability (331.78 and 295.45 F g(-1) at 0.5 and 10 A g(-1), respectively), and good durability (98% capacitance retention a ft er 10000 galvanostatic charge/discharge cycles at 10 A g(-1) in the two-electrode system) in 6 M KOH. Additionally, corn- and black soybean-derived porous carbons were prepared to undergo the same procedures, showing excellent capacitive performance as well. Therefore, biomass-derived nanocarbons with the MgCl2 activation strategy show a promising future for application as a supercapacitor.