Photopolymerized hydrogels from poly(ethylene glycol) dimethacrylate (PEGDM) and similar derivatives have been extensively used as scaffolds for tissue regeneration and other biological applications. A systematic investigation into the structure and mechanical properties of PEGDM hydrogels was performed to characterize the relationships between the network structure and gel properties. Gels were prepared from oligomers of different molecular masses (1000-8000 g/mol) at various concentrations. Small-angle neutron scattering was used to characterize the structural features of hydrogels with respect to their semidilute solution precursors. A well-defined structural length scale manifested as a maximum in the scattering intensity was observed for hydrogels derived from high molecular mass PEGDMs and/or high oligomer mass fractions. Mechanical testing showed that PEGDM hydrogels are mechanically robust, consistent with gel structures that contain reinforcing cross-linked clusters. Shear moduli were determined for hydrogels swollen to various degrees in water. The concentration dependence of shear modulus for these nonideal hydrogels exhibits a power law behavior with an exponent close to (1)/(3).