Two new sodium nickel phosphates, Na5Ni2(PO4)(3)center dot H2O (I) and Na6Ni2(PO4)(3)OH (H), have been synthesized hydrothermally and characterized by synchrotron X-ray diffraction, electron diffraction, low-temperature thermodynamic and magnetic measurements, and ab initio calculations. Unlike the majority of Ni2+ compounds, I and II show predominant ferromagnetic exchange couplings. I crystallizes in the monoclinic space group P2(1)/n (a = 14.0395(4) angstrom, b = 5.1847(14) angstrom, c = 16.4739(4) angstrom, beta = 110.4186(14)degrees) and features chains of ferromagnetically coupled Ni2+ ions. In II with the orthorhombic space group Pcmb (a = 7.5007(15) angstrom, b = 21.4661(4) angstrom, c = 7.1732(15) angstrom), the ferromagnetically coupled Ni2+ ions form dimers arranged on a spin ladder. Both compounds represent rare examples of quasi-one-dimensional ferromagnets. Structural features behind this unusual magnetic behavior are discussed.