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The nanocrystalline (Na0.7K0.3)0.5Bi0.5TiO3 plates present room temperature ferromagnetism.The reduction of ferromagnetism for the (Na0.7K0.3)0.5Bi0.5TiO3 plate with subsequent long time and high temperature air-annealing indicates that the observed ferromagnetism is connected with the cation vacancies at/near the surface of nanograins.We check the role of cation or anion vacancies in introducing ferromagnetism through the comparison of magnetization values between air and vacuum atmosphere annealing.The results of density functional theory calculation with the local density approximation plus on-site effect method on the magnetism of (Na2/3K1/3)0.5Bi0.5TiO3 supercell show that Na vacancies can introduce a nonzero magnetic moment (as shown in Fig.1),which is similar with the magnetic moment found in Na0.5Bi0.5TiO3 (100) surface[1].In addition,the electric field treatment leads to an enormous enhancement of saturation magnetization for (Na0.7K0.3)0.5Bi0.5TiO3 plates,showing a strong magnetoelectric coupling[2].