Fe-substituted manganese dioxide (Mn1-xFexO2, x=0, 0.1, 0.3 and 0.4) nanoparticles were hydrothermally prepared. X-ray diffraction (XRD) analysis showed the γ-phase of MnO2 in all of samples. The presence of Fe was detected by elemental analysis with a X-ray fluorescence (XRF) spectrometer. Field-emission scanning electron microscopy (FE-SEM) images showed the size and morphology of Mn1-xFexO2 became small. The higher specific surface area of samples with increasing content of Fe was confirmed with Brunaure-Emmett-Teller (BET) method. In electrochemical tests, the Mn1-xFexO2-δ (x=0,0.1,0.3 and 0.4) electrode showed the smaller discharge capacity with increasing content of Fe (180 and 70 in x=0 and 0.4, respectively) in the 1st discharge. In addition, the Fe-substitution led to slightly improve the irreversible capacity, but the poor cycleability.