The objective of this chapter presents the mechanical characterization of fused deposition modeling (FDM) as a famous and the most used technology in 3D printing or rapid prototyping process. The availability and cheapness of raw materials and the simplicity of these types of printers have led to their widespread use for various applications. In contrast, there are challenges in this method, like other methods of additive manufacturing (AM), one of the most important of which is the selection of print parameters and its impact on mechanical properties significantly. In this chapter, three subject are discussed; thermoplastic filament used, introduction of printing parameters and the impact of them on mechanical properties. Due to the widespread use of various thermoplastic filament as raw materials for FDM printers, the most widely used ones are introduced. Then the strong impact of the FDM printing parameters on the mechanical properties of produced specimens is fully explored as the main topic of this chapter.