Solid solutions formed between the cubic spinel LiMn2O4 and the ordered spinel Li0.5Fe2.5O4 have been investigated by X-ray powder diffraction, infrared spectroscopy and magnetic techniques. The series shows a spinel structure with the unit-cell constant increasing from a = 8.209 Angstrom to a = 8.335 Angstrom, with the increasing Fe/(Fe + Mn) ratio. For 0 less than or equal to Fe/(Fe + Mn) less than or equal to 0.6 the cubic spinel structures (space group Fd3m) were formed, while in samples with higher Fe content the ordering of lithium ions leads to the lowering of symmetry (space group P4,32). The measurements of integrated intensities of X-ray reflections show the distribution of Li+ ions in both octahedral and tetrahedral cationic positions of spinel lattice, although the end-members of the series, LiMn2O4 and LiFe5O8, contain Li+ coordinated tetrahedrally and octahedrally, respectively.