Microstructure, dielectric and impedance characterizations of magnetoelectric (1-x)Sr0.5Ba0.5Nb2O6/xCoFe(2)O(4) composite ceramics were investigated thoroughly. Thermally activated Maxwell-Wagner polarization was adopted to be the main explanation of the high dielectric constant in the title composite ceramics. The broad dielectric constant step was observed in the composite ceramics with x = 0.3 and 0.4 over a certain temperature interval around room temperature. Such temperature-independent step was interpreted through the balance between the phase transition of the relaxor ferroelectric matrix and thermally activated Maxwell-Wagner mechanism of the composite ceramics. The dielectric constant of the composite ceramics was fitted using the combination of thermally activated Maxwell-Wagner polarization and modified Curie-Weiss law. (C) 2009 Elsevier B.V. All rights reserved.