Sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs) have attracted increasing attention due to the high cost and finite abundance of lithium. Here, by using first-principles calculations, monolayer β-GeSe has been found to be a promising anode material with a capacity of 353.65 mA h g⁻¹ for both NIBs and KIBs. Additionally, the diffusions of Na and K over the monolayer β-GeSe are ultrafast with small energy barriers of 0.080/0.125 eV and 0.052/0.047 eV for the Ge/Se side, respectively, indicating excellent rate performance. Monolayer β-GeSe has low open circuit voltages of 0.219 V (vs. Na/Na⁺) and 0.030 V (vs. K/K⁺), which implies that the NIBs and KIBs could have high energy densities due to the high working voltages between the anode and cathode. Therefore, monolayer β-GeSe as an anode material for NIBs and KIBs with excellent performance shows tremendous potential in the energy field.