An out-put only modal parameter identification method based on variational mode decomposition (VMD) is developed for civil structure identifications.The recently developed VMD technique is utilized to decompose the free decay response (FDR) of a structure into to modal responses.A novel procedure is developed to calculate the instantaneous modal frequencies and instantaneous modal damping ratios.The proposed identification method can straightforwardly extract the mode shape vectors using the modal responses extracted from the FDRs at all available sensors on the structure.A series of numerical and experimental case studies are conducted to demonstrate the efficiency and highlight the superority of the proposed method in modal parameter identification using both free vibration and ambient vibration data.The results of the present method are compared with those of the empirical mode decompositionbased method,and the superiorities of the present method are verified.The proposed method is proved to be efficient and accurate in modal parameter identification for both linear and nonlinear civil structures,including structures with closely spaced modes,sudden modal parameter variation,and amplitude-dependent modal parameters,etc.