The nanotechnology field originated in the 21 ^st century. Especially 2D-based nanomaterials have received a lot of attention since they are easily affordable, nontoxic, and have excellent electrical, optical, thermal, and mechanical properties. Moreover, it is simple to synthesize and can be applied to a wide range of applications. The present chapter mainly focuses on various types of synthesis methods for 2D nanomaterials using top-down strategies. Many top-down strategies have been developed to synthesize 2D nanomaterials, such as etching, mechanical milling, sputtering, and laser ablation. In all methods, we would introduce their synthesis parameters, advantages, disadvantages, and applications. Moreover, its characterization and toxicity were briefly introduced.