In this work, a biodegradable and biocompatible nanocomposite hydrogel was successfully prepared on basis of nanoclay and polyethylene-glycol diacrylates (PEGDA). The physical interspersing between nanoclay particles and PEG chains combined with the chemical crosslinking within the PEG networks endowed the obtained nanocomposite hydrogels with enhanced mechanical properties in comparison with pure PEG hydrogels. Simultaneously, the incorporation of nanoclay to the PEGDA/nanoclay (PEGDA-Clay) nanocomposite hydrogel not only improved the adsorption and spreading ability of cells on the hydrogels, but also effectively facilitated the in vitro osteogenic differentiation of primary rat osteoblasts due to the sustainable release of magnesium ions (Mg2+) and silicon ions (Si4+) from the PEGDA-Clay nanocomposite hydrogel. In addition, the implantation of the PEGDA-Clay nanocomposite hydrogels in the tibia defects of Sprague-Dawley rat could promoted the new bone formation efficiently, further suggesting the excellent osteogenic ability of PEGDA-Clay nanocomposite hydrogel. We expect that this kind of biocompatible nanocomposite hydrogels with attractive mechanical properties and a variety of bioactive osteogenic ions will offer a new possibility for bone tissue regeneration.