The crystallization kinetics of Bi0.5Y2.5Fe5O12 powders prepared by the coprecipitation process have been investigated. The activation energy of crystallization was calculated on the basis of differential scanning calorimetry at different heating rates. Analysis of nonisothermal DSC data yielded a value of 823.8 kJ/mol and 2.25 for the activation energy of crystallization and the Avrami exponent, respectively. This value for the Avrami exponent was consistent with surface and internal crystallization occurring simultaneously. The complex permittivity and permeability of Bi0.5Y2.5Fe5O12 was measured at the X-band (8-12 GHz) using the cavity perturbation technique. For dielectric properties, the real part of permittivity, epsilon', was obtained in the range of 13.57- 16.37. For magnetic properties, the real part of permeability, mu', was obtained in the range of 21.61-16.90.