Co-Fe layered double hydroxides at different Fe/Co ratios were synthesized from brucite-like Co1-x2+Fex2+(OH)(2) (0 < x < 1/3) via oxidative intercalation reaction using an excess amount of iodine as the oxidizing agent. A new redoxable species: triiodide (I-3(-)), promoted the formation of single-phase Co-Fe LDHs. The results point to a general principle that LDHs with a characteristic ratio of total trivalent and divalent cations (M3+/M2+) at 1/2 may be the most stable in the oxidative intercalation procedure. At low Fe content, e.g., starting from Co1-x2+Fex2+(OH)(2) (x < 1/3), partial oxidation of Co2+ to Co3+ takes place to reach the M3+/M2+ threshold of 1/2 in as-transformed Co-2/3(2+)-(Co-1/3-x(3+)-Fe-x(3+)) LDHs. Also discovered was the cointercalation of triiodide and iodide into the interlayer gallery of as-transformed LDH phase, which profoundly impacted the relative intensity ratio of basal Bragg peaks as a consequence of the significant X-ray scattering power of triiodide. In combination with XRD simulation, the LDH structure model was constructed by considering both the host layer composition/charge and the arrangement of interlayer triiodide/iodide. The work provides a clear understanding of the thermodynamic and kinetic factors associated with the oxidative intercalation reaction and is helpful in elucidating the formation of LDH structure in general.