Hydrogels are cross-linked, water-swollen polymer networks that are widely used as a biomaterial. Because of high amount of water, they are mechanically poor and soft. This aspect limits their applications. The suitability of hydrogels as biomedical materials, especially as drug delivery systems depend on their bulk structure. The most important parameters used to characterize the network structure of hydrogels are the polymer volume fraction in the swollen state, the molecular weight of the polymer chain between two neighboring crosslinking points, and the corresponding mesh size. Among hydrogel matrixes HEMA (hydroxyl ethyl methacrylate) base hydrogels are of great interest and they have many applications in biomedical fields like artificial organs and drug delivery system. The stiffness of this family of hydrogels is tunable by changing water ratio during polymerization. The goal of this project is to calculate the mesh size of this hydrogel through rubber elasticity theory formulation, which involved interesting experimental works to measure required parameters for this calculation. Experiments consist of hydrogel synthesize via UV polymerization, measuring swelling ratio, polymer volume fraction, polymer density measurement through bouncy technique and measuring elastic modulus of hydrogels in tension. Each experiment provides the operator with fundamental skills in hydrogels characterization for who are interested to work with hydrogels in any biomedical application.