The equation " eff / ð c À Þ Às which shows the relationship between effective dielectric constant (" eff ) and the filler concentration ('), is widely used to determine the percolation behavior and obtain parameters, such as percolation threshold ' c and the power constant s in conductor-dielectric composites (CDCs). Six different systems of CDCs were used to check the expression by fitting experimental results. It is found that the equation can fit the experimental results at any frequency. However, it is found that the fitting constants do not reflect the real percolation behavior of the composites. It is found that the dielectric constant is strongly dependent on the frequency, which is mainly due to the fact that the frequency dependence of the dielectric constant for the composites close to ' c is almost independent of the matrix.