Lithium titanium oxide spinel, Li[Li1/3Ti5/3]O4 (LTO), is a zero-strain lithium insertion material, which indicates a virtually 0% change in lattice volume (ΔV) during the electrochemical reaction. We have performed systematic structural and electrochemical studies on Li1/2+x/2Fe5/2−3x/2Ti x O4 (LFTO) with 0 ≤ x ≤ 1.666, where the LFTO formula forms a series of spinel compounds with Fe[Li1/2Fe3/2]O4 and LTO via Li1/2Fe1/2[Li1/2Fe1/2Ti]O4. The LFTO samples with x < 0.875 underwent a typical conversion reaction with large discharge capacities above ∼500 mAh g−1, similar to nano-sized metal oxides. The LFTO samples with 0.875 ≤ x < 1.666 maintained their cubic lattice parameter (a c) during the discharge and charge reactions. Since the Δa c and ΔV values were lower than +0.2 and +0.5%, respectively, these LFTO samples are also regarded as zero-strain lithium insertion materials. Surprisingly, ex situ X-ray diffraction measurements revealed a reversible decrease/increase in the intensities of the 111 and 311 diffraction lines, indicating that Fe ions shuttle back and forth between the tetrahedral and octahedral sites of the spinel lattice. This reaction scheme differs from the so-called topotactic reaction, where only Li+ ions are mobile and transition metal ions are immobile. Details of the non-topotactic reaction for LFTO are presented.