Phosphating manganese oxide (PMn) nanosheet arrays were synthesized via a facile and fast cathodic electrodeposition and following cyclic voltammetry phosphating as binder-free electrode materials for supercapacitors application. The morphology, chemical composite and structure characteristic of PMn nanosheets confirm that phosphate ions have been introduced to the surface of Mn3O4 nanosheets successfully. The as-prepared PMn electrode shows excellent electrochemical properties in 0.1M Na2SO4 aqueous solution with a three-electrode system. The optimal specific capacitance of the PMn nanosheet arrays electrode at 5mVs(-1) (6.7mFcm(-2)) is superior to that of the Mn3O4 nanosheets electrode (2.7mFcm(-2)). Furthermore, the specific capacitance of obtained PMn nanosheets electrode reaches a retention of 87.6% after 5000 charge-discharge cycles at 0.08mAcm(-2), indicating great cycling stability. Therefore, modification of phosphate ions can effectively suppress the dissolution of manganese oxide and achieve a significant improvement in electrochemical property for supercapacitors with a manganese oxide electrode.