Bi2O3 (BT) is considered a fascinating anode material for asymmetric supercapacitors (ASCs) due to its high theoretical capacity, but the low conductivity limits further applications. With this in mind, cerium-doped Bi2O3 (Ce−BT) nanoflower spheres were synthesized by a facile and rapid microwave-assisted solvothermal method for ASCs anode materials. It is found that the morphology of BT could be controlled by Ce doping from stacked nanosheets to well-dispersed nanoflowers spheres and producing abundant amorphous regions, thus expediting the ion transport rate. Consequently, When the added Bi to Ce molar ratio is 40:1 (Ce-BT-40), it exhibited a specific capacitance of 721 F g−1 at 0.5 A g−1. Additionally, when fabricating ASCs with as-prepared Ce−BT−40 and CeNiCo-LDH, an energy density of 59.1 Wh kg−1 is provided at a power density of 652 W kg−1. This work not only reveals the mechanism of the effect of Ce doping on the electrochemical properties of BTs but also proposes a rapid synthesis method of Ce−BTs by microwave-assisted solvent method, which provides new insights for building advanced ASCs with high energy density and low cost.