To provide electrolytic manganese dioxide to be used as a cathode active material for an alkali-manganese dry cell, which has a high alkali potential and is provided with a high reactivity and packing efficiency as a cathode for the cell. Electrolytic manganese dioxide having an alkali potential of at least 310 mV, FWHM of at least 2.2 DEG and at most 3.0 DEG , and a (110)/(021) peak intensity ratio in the X-ray diffraction peaks of at least 0.50 and at most 0.80, is used. The (110) interplanar spacing of the electrolytic manganese dioxide is preferably at least 4.00 AA and at most 4.06 AA. Particularly when the alkali potential is at least 350 mV and at most 400 mV, the molar ratio of structural water contained (H 2 O/MnO 2 ) is preferably at least 0.20. It can be produced by electrolysis at a low sulfuric acid concentration at the initial stage of the electrolysis and at a high sulfuric acid concentration at a later stage. It is preferred to further carry out sulfuric acid treatment.