The sodium-iron phosphate maricite-NaFe0.9Mn0.1PO4 was synthesized using the ball mill method. The crystal structure and magnetic properties of the prepared materials were studied using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectroscopy. Structural refinement of maricite-NaFe0.9Mn0.1PO4 was analyzed using the FullProf program. From the XRD patterns, the crystal structure of maricite-NaFe0.9Mn0.1PO4 was found to be orthorhombic with the space group Pmnb. The lattice parameters of maricite-NaFe0.9Mn0.1PO4 are as follows: a0 = 6.866 Å, b0 = 8.988 Å, c0 = 5.047 Å, and V = 311.544 Å3. Maricite-NaFePO4 has an edge-sharing structure that consists of FeO6 octahedral. Under an applied field of 100 Oe, the temperature dependences of zero-field-cooled (ZFC) and field-cooled (FC) curves were measured from 4.2 to 295 K. Mössbauer spectra were also recorded at various temperatures ranging from 4.2 to 295 K. We thus confirmed that the Néel temperature of NaFe0.9Mn0.1PO4 (TN = 14 K) was lower than that of maricite-NaFePO4 (TN = 15 K).