Nickel oxide(NiO) powder is prepared by decomposition of basic nickel carbonate (mNi(OH)(2).nNiCO(3).xH(2)O) in microwave field with NiO seed as a microwave absorbing additive. Basic nickel carbonate(BNC) can decompose completely to NiO powder in a short time. Firstly, the heat for BNC decomposition is provided by NiO seed which absorbs microwave and then by NiO product which also absorbs microwave. The decomposition process of BNC can be accelerated by increasing the amount of BNC, the amount of NiO seed or the microwave field power. The size of NiO powder product is about 180nm when the size of BNC used is about 160nm.