We synthesized monodisperse nanospheres of an intermetallic FeSn5 phase via a nanocrystal-conversion protocol using preformed Sn nanospheres as templates. This tetragonal phase in P4/mcc space group, along with the defect structure Fe0.74Sn5 of our nanospheres, has been resolved by synchrotron X-ray diffraction and Rietveld refinement. Importantly, FeSn5, which is not yet established in the Fe-Sn phase diagram, exhibits a quasi-one dimensional crystal structure along the c-axis, thus leading to interesting anisotropic thermal expansion and magnetic properties. Magnetization measurements indicate that nanospheres are superparamagnetic above the blocking temperature T-B = 300 K, which is associated with the higher magnetocrystalline anisotropy constant K = 3.33 kJ m(-3). The combination of the magnetization measurements and first-principles density functional theory calculations reveals the canted antiferromagnetic nature with significant spin fluctuation in lattice a-b plane. The low Fe concentration also leads Fe0.74Sn5 to enhanced capacity as an anode in Li ion batteries.