Summary: The dynamic substructure method is extended to non-conservative systems. The substructure fixed-interface flexibility is expressed in its natural modes. The formulation includes conservative and dissipative systems as special cases. To accelerate the convergence with respect to the partial modes, the flexibility is separated into modal contributing and static contributing parts. Inverse iteration is used to find the non-defective system modes. The parameters which make the system matrix defective are determined by the Newtonian algorithm and the derivatives of determinants are given explicitly.