A nickel coating on the surface of alumina particles, used as a reinforcement in metal-ceramic composite materials, its dielectric and electromagnetic properties have important application value. In this paper, nickel was deposited on alumina powder surface by the way of hydrothermal and sintering. The results showed that the nickel powders were fcc structure. The size of the crystal grains ranged from 10 nm-50 nm. The electro-magnetic characteristics were measured by HP 8722ES microwave net work analyzer in the band of 2-18 GHz. It was showed that both the Ni-Al203 and Co-Al203 nanopowders had low dielectric constant, low electromagnetic and good properties in microwave absorption.