LiNi0.5Mn1.5O4 is suitable for electrochemical applications as an active material. This material has capability for high rate application in Li-ion battery. In this research, the diffusion mechanism of Li ions in LiNi0.5Mn1.5O4 was studied by chronoamperometry technique and computer simulation (ab initio and Fickian approach). According to the results, two bulk diffusion constants were calculated for LiNi0.5Mn1.5O4 during intercalation or deintercalation. At low concentration of Li ions in LiNi0.5Mn1.5O4, the diffusion constant was about 10−9 cm2/s and for other Li ions concentration, it was about 10−11 cm2/s. In addition, the diffusion constant at the surface of LiNi0.5Mn1.5O4 was estimated 10−8 cm2/s by a semi empirical model. So, the diffusion constant of Li ions in LiNi0.5Mn1.5O4 has been estimated in the range of 10−8 to 10−11 cm2/s.