In this paper, we develop a robust reduced-order modeling method, named algebraic dynamic condensation, which is based on the improved reduced system method. Using algebraic substructuring, the global mass and stiffness matrices are divided into many small submatrices without considering the physical domain, and substructures and interface boundary are defined in the algebraic perspective. The reduced model is then constructed using three additional procedures: substructural stiffness condensation, interface boundary reduction, and substructural inertial effect condensation. The formulation of the reduced model is simply expressed at a submatrix level without using a transformation matrix that induces huge computational cost. Through various numerical examples, the performance of the proposed method is demonstrated in terms of accuracy and computational cost. Copyright (c) 2016 John Wiley Sons, Ltd.