Highly crystallized mullite composite has been synthesized at 1000 degrees C and 1300 degrees C via sol gel technique in the presence of transition metal ions such as cobalt, nickel and copper. The dielectric properties (dielectric constant, loss tangent and a.c. conductivity) of the composites have been measured at room temperature and their variation with increasing frequency and concentration of the doped metals has been investigated. The composite doped with nickel exhibits minimum dielectric constant of 3.15 at 0.002(M) concentration at a frequency of 1.5 MHz. Experimental data shows a linear increase in a.c. conductivity with increasing concentration of metal doping ions. The dielectric constant and loss tangent of the composites are within the range of requirements for commercial use in electronics. (C) 2012 Elsevier B.V. All rights reserved.