The parametric instability of heterogeneous orthotropic truncated conical shells under time dependent axial compressive load on the basis of Donnell shell theory is investigated. The dynamic basic equations are reduced into a Mathieu-Hill type differential equation describing the instability of heterogeneous orthotropic truncated conical shells using Galerkin's method. The backward and forward excitation frequencies are determined by using Bolotin's method. A comparison with the previous studies has been developed in order to validate the present results. The effects of axial load factors, heterogeneity, orthotropy, as well as the variation of the characteristics of the conical shell on the backward and forward excitation frequencies are studied in detail.