A study was made of the electron paramagnetic resonance (EPR) in electrolytically and chemically prepared manganese dioxides intended for use in power sources. A typical EPR signal for the powdered MnO2 samples is wide single line with g = 1.94. The replacement of some Mn4+ ions by Mn3+ modified the character of the exchange interaction. A correlation was established between the width of the EPR signal and the ionic conductivity value as well as Mn3+/Mn4+ ratio and OH- groups contents in the samples. It is supposed that the EPR data can be useful for the semiquantitative expression of chemical and electrochemical activity of different MnO2 samples. In some samples EPR signals with g = 2.000, A = 8.81 mT (A is hyperfine structure parameter) were revealed due to the presence of MnSO4 water solutions traces.