Nanosized MnO 2 powders were grown using a green synthesis based on citrates via redox reaction between KMnO 4 and natural reducing agents, i.e. lemon juice and peel extracts, without generating hazardous waste. X-ray diffraction (XRD) and Raman studies show that the samples grow as cryptomelane polymorph, α-MnO 2 , crystallized with the tetragonal cryptomelane structure. Both J-MnO 2 prepared from lemon juice and P-MnO 2 prepared from citrus peel consist of nanosized particles as observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thermogravimetric analysis (TGA) confirms the typical thermal decomposition of MnO 2 at temperatures of up to 500 ° C. Improved electrochemical properties are obtained and discussed for P-MnO 2 , with a reversible capacity that reaches 160 mAh g-1 (initial capacity of 212 mAh g-1) at a current density of 10 mA g-1 and a good rate capability.