Ternary mixtures of equi-density particles have been fluidized in a gas-solid fluidized bed to study the mixing characteristics. A correlation for the mixing index has been developed for these mixtures. The mixing index for the ternary mixtures has also been calculated by the already available method. Finally a comparison has been made for the values of the mixing index calculated by both the methods against the experimental ones. The values of the mixing index for the ternary mixtures thus obtained have also been compared with those of the binary mixtures thereby indicating its application for real life multi-component mixing over a wide range of parameters.