In this paper the development of interactive and comparative dynamic characteristic identification software titled as the ModalCAD is described. The software is developed for vibration monitoring of civil engineering structures and constructed by using MATLAB, which is a mathematical tool developed by The Mathworks. The modal analysis of structures consists of four distinct steps: Data collection, digital signal processing, determination of the modal parameters (eigenfrequencies, damping ratios, mode shapes, and modal scaling factors) with modal data presentation/validation and model updating. The ModalCAD software is a powerful tool that deals with modal parameter identification and validation procedure. The ModalCAD offers extensive functionalities for the visualization and processing of the measurement data, the identification of system models, and the determination and visualization of the structure's modal parameters. The program disposes of a graphical user interface, which what makes it very intuitive and easy to handle. The most common modal parameter estimation techniques have been used in the ModalCAD. The Operating Vectors method, Complex Exponential method, and Polyreference Time Domain method are implemented in a user-friendly way. By pushing buttons the user is guided through the whole process of input-output and output-only modal analysis: Preprocessing the data, system identification, extracting modal parameters, animating mode shapes, and evaluating model validation tools. The possibilities of the program are demonstrated with a three dimensional frame model. It can be said that the ModalCAD software can be used as a scientific tool in future structural health monitoring studies of researchers.