The solid-state reaction was adopted to prepare a series of LiCo1-xMgxO2 powders doped with different amount of Mg2+. The XRD patterns reveal single phase for all the prepared materials. The shift of the electronic structure of LiCo1-xMgxO2 has been investigated by X-ray photoelectron spectroscopy to confirm the single phase for material. Influence of dopant amount on the electromagnetic properties of LiCoO2 powders was analyzed. The dielectric and the microwave absorption properties were evaluated. Results showed that with the increase in Mg the complex permittivity decreased after increasing. Maximum values of both real part (epsilon=16.2 at 8.2GHz) and imaginary part (epsilon=4.1 at 8.2GHz) were obtained for x=0.06. Monolayer absorbent containing 75wt% LiCo0.94Mg0.06O2 had the peak microwave absorption properties in a thickness of 2.1mm. The available bandwidth (<-10dB) was obtained in 8.4-10.2GHz and the minimum reflection loss was -50.4dB, which indicated that LiCo1-xMgxO2 powders would be potential materials as microwave absorption.