The mixed ferrites Li0.5-0.5xCu-Fe(2.5-2.5)xO(4) (where x = 0 to 1) were prepared by the ceramic method. Infrared (IR) absorption and dielectric properties were used to investigate this ferrite. The IR spectra in the range from 200 to 1000 cm(-1) were reported. Mainly, two bands were observed. The band at around 575 cm(-1) (nu(1)*) and the band at around 385 cm(-1) (nu(2)*) were assigned to the tetrahedral and octahedral complexes, respectively. A small band at about 325 cm(-1) (nu(3)) indicated the presence of octahedral divalent metal-oxygen in complexes. This band decreases with the increase of copper concentration and completely disappears at sample of x greater than or equal to 0.3. The threshold frequency for the electronic transition was determined. It was found that the threshold frequency for electronic transition seems to be decreasing with increasing Cu2+ content. The a.c. conductivity <(sigma)over bar> and dielectric properties (dielectric constant epsilon', dielectric loss epsilon ") were measured at room temperature as a function of frequencies from 10(2) to 10(6) Hz. Also, the variation of loss tangent (tan delta) with frequency was measured. It was found that the maximum values of <(sigma)over tilde> lies in the range of frequency corresponding to the peaks of tan delta. The sample of x = 0 shows a maximum value of a at f(max) = 2 x 10(5) Hz. The relaxation time (tau) was calculated for the sample of x = 0 and 0.5 and it was found to be 3.5 x 10(-6) and 5 x 10(-6) s, respectively. The electrical conduction mechanism was explained in terms of the electron hopping model. The frequency exponential factor (s) was estimated and it was found to vary between 0.4 and 0.8.