The use of Mg in rechargeable batteries can be competitive with Li in terms of economy, safety, environment and capacity. In contrast to lithium and sodium, the compounds with NASICON-type structure have received little attention as hosts for reversible magnesium insertion. The selection of the electrolyte solution and voltage window seems to be crucial for controlling sodium/magnesium (de) insertion. Here, Na3V2(PO4)(3) (NVP) has been tested as a positive electrode vs. Mg metal with 0.5 M magnesium bis(trifluoromethanesulfonimide) in 1,2-dimethoxyethane as electrolyte solution, and the mechanism of the charge/discharge process has been studied. In magnesium cell, firstly sodium is partially deinserted from the framework of NVP up to ca. Na1.3V2(PO4)(3) through a single voltage-plateau at 1.7 V, the cell of the crystal lattice is contracted, and a magnesium-sodium hybrid electrolyte is formed in situ. Secondly, sodium and magnesium are inserted through two consecutive voltage-plateaus at 1.6 and 1.2 V, respectively, while the main framework is preserved and the lattice is expanded. With further charge-discharge cycling, only one discharge plateau is observed at 1.2 V due to insertion of magnesium. If sodium ions are removed from the electrolyte solution after the first charge, only magnesium is inserted in the NASICON-type framework during the discharge. The electrochemical behavior of this material as electrode in magnesium battery is very promising, providing a reversible capacity of ca. 60 mAh g(-1) after 100 cycles. (C) 2017 Elsevier Ltd. All rights reserved.