Pb[(Mg3/4Co1/4)(1/3)Nb-2/3]O-3 (PMCN) ceramic was prepared by a columbite precursor method. The structural analysis revealed the cubic phase of PMCN at room temperature. Dielectric studies of the compound indicated the relaxor behaviour with diffuse phase transition (DPT). The transition temperature (T-m) was found to be at -22 degrees C at 1 kHz. The frequency dependence of T-m has been modeled using Vogel-Fulcher relation. The dielectric relaxation in PMCN is found analogous to the magnetic relaxation in spin-glass system. Complex impedance analysis indicated multi-Debye-type dielectric relaxation in PMCN and relaxation frequency shifts to higher frequencies with the increase in temperature. (c) 2005 Elsevier B.V. All rights reserved.