Molybdenum (Mo)-doped vanadium dioxide (VO$_2$(B)) nanobelts were successfully synthesized using commercial vanadium pentoxide (V$_2$O$_5$) as the starting material and ammonium molybdate as the dopant by a simple hydrothermal route. Then, Mo-doped VO2(B) nanobelts were transformed to Mo-doped V$_2$O$_5$ nanobelts by calcination at 400$^{\circ}$C under an air atmosphere. The samples were characterized by X-ray powder diffraction,energy-dispersive X-ray spectrometer, elemental mapping, X-ray photoelectron spectroscopy, X-ray fluorescence and transmission electron microscopy techniques. The results showed that Mo-doped VO$_2$(B) and V$_2$O$_5$ solid solution with high purity were obtained. The electrochemical properties of Mo-doped VO$_2$(B) and V$_2$O$_5$ nanobelts as supercapacitor electrodes were measured using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD). The specific capacitance of VO$_2$(B) nanobelts slightly declines with Mo doping, however, the specific capacitance of V$_2$O$_5$ nanobelts greatly improves with Mo doping. Mo-doped V$_2$O$_5$ nanobelts exhibit the specific capacitance as high as 526 F g$^{−1}$ at the current density of 1 A g$^{−1}$. Both CV and GCD curves show that they have good rate capability and retain 464, 380, 324 and 273 F g$^{−1}$ even at a high-current density of 2, 5, 10 and 20 A g$^{−1}$, respectively. It turns out that Mo-dopedV$_2$O$_5$ nanobelts are ideal materials for supercapacitor electrodes in the present work.