This paper describes a MATLAB based SDM software embodied in a GUI environment (SDMTool), which is a technical high-end tool for structural dynamics modification (SDM) problems. The software is composed of four modules: 1) FE model linker module; 2) FE model updating module; 3) SDM forward problem module; 4) SDM structural optimization module. The software can be useful to engineers performing researches on structural dynamics modification and FE model updating.