Lithium rich and deficient, Li1+x Ni0.4+yCo0.3Mg0.3O2 (x =0, ± 0.1, -0.2 and y = 0, ± 0.05, +0.1) cathode materials were prepared by conventional solid state reaction method. Vibrational studies of the prepared materials were analyzed by using FTIR spectroscopy. Electrical and dielectric properties of the materials were measured using AC impedance spectroscopy in the frequency range 7 MHz-1Hz over the temperature range of 303-343 K. The sample Li0.9Ni0.45Co0.3Mg0.3O2 shows maximum conductivity of 1.02 x 10-4 S cm-1 at ambient temperature. All samples obey Arrhenius rule. Dielectric properties of the cathode materials on the influence of Li, Ni composition and temperature were also discussed.