► Electrochemical features of both maricite and olivine NaFePO 4. ► Full insertion of Na achieved at 1.7 V, capacity retention of 147 mAh g −1 in olivine. ► Na insertion/de-insertion operates in a two-phase process. ► XRD and EDX analysis of intermediate compositions. We report the electrochemical properties of submicron-sized particles of NaFePO 4. Two materials have been studied and characterized by XRD, SEM, EDX, EIS and Raman experiments: the maricite phase synthesized by hydrothermal method and the olivine phase obtained from delithiation of LiFePO 4. NaFePO 4 materials have an electrochemical activity in Na cell using NaPF 6–EC–DEC electrolyte, but only in the heterosite phase, and the capacity is reduced already in the second cycle. The two-phase system at intermediate compositions has also been analyzed.