Expansion joints are the most basic parts of piping systems that are used in various industries such as powerhouses, petrochemical and aerospace industries. The expansion joint is used for absorption of mechanical and thermal displacements in piping systems. Bellows is the main part of an expansion joint. Bellows are essentially flexible elements of expansion joints. These are usually made from austenitic stainless steels that show good weldability, formability, creep and corrosion resistance, strength and fracture toughness. The bellows can be made by various methods such as hydroforming, punch and roll forming methods. In hydroforming a tube is placed in a hydrolic press or bellows forming machine. Circular external die ring of suitable countour are placed outside the tube at longitudinal intervals approximately equal to the developed length of the completed convolutins. The tube is filled with a medium such as water and pressurized until circumferential yielding occurs this forming operation continues with a simultaneas circumferential yielding and controlled longitudinal shortening of the tube until the proper configuration is obtained. Individual or multiple convolutions may be formed by this method. Depending on the bellown configuration, several partial-forming steps with intermediate heat treatment may be required. Reinforced bellows may be formed by utilizing external reinforcing rings that act as part of the forming dies. After completion, when the dies are removed, the rings remain as an integral part of the bellows. In this thesis first explains various types of expansion joints and their application. Then past research on bellows are reviewed. In the next chapters of this thesis various forming method of bellows are described. Then attention is paid on hydroforming method of metal bellows and effective parameters on this method are focused. In the present work, the latter half processes including the tube-bulging, folding and springback are analyzed consistently using the FEM. The main objective of this study is to find the effect of process parameters on the one- layer and two- layer metal bellows properties. Parameters such as the geometry and dimensions of bellows, die course and pressure of forming. For this purpose, two samples of single-layer and double layer Bellows were made.The finite element model has been used to simulate hydroforming of bellows(with ABAQUS/Explicit 6.10) and at the end the results were compared with those made. The model has been confirmed by experimental. The simulation results showed good agreement with experimental test. Keywords : Bellows, Expansion Joint, Hydroforming, Finite Element Method