Comparative study of the solid-state redox reactions of LiCo1/4Ni3/4O2 and LiAl1/4Ni3/4O2 was carried out by XRD and electrochemical methods. XRD examinations indicated that the reactions proceeded in single phase for both samples. The change in interlayer distance between MeO2-sheets for LiCO1/4Ni3/4O2 or LiAl1/4Ni3/4O2 was almost the same as that for LiNiO2 in the region 0 < x 1 3/4 in Li1-xMeO2 (Me=Ni, Co1/4Ni3/4, Or Al1/4Ni3/4) Reversible potentials as a function of x were measured and the solid-state redox reactions involving in the lithium insertion reactions were characterized by using simple equations to describe the redox potentials. According to our results, substitution of aluminum for nickel in LiNiO2 raised the levels of solid-state redox potentials primarily derived from nickel species by about 0.1 V, while the substitution of cobalt did not affect the solid-state redox potentials in that range. Differences and similarities between the solid-state electrochemical reactions of LiCo1/4Ni3/4O2 and LiAl1/4Ni3/4O2 were discussed therefrom.