Magnetically responsive hydrogel networks based on composites of magnetic nanoparticles and temperature responsive hydrogels were developed. These systems show great promise as active components of microscale and nanoscale devices and are expected to have a wide applicability in various biomedical applications. Specifically, nanocomposite hydrogel systems based on the temperature sensitive N-isopropylacrylamide hydrogels crosslinked with ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and poly(ethylene glycol) 400 dimethacrylate (PEG400DMA) were synthesized and characterized. The composite systems were synthesized by UV free-radical polymerization. Iron oxide magnetic nanoparticles were incorporated into the hydrogel systems by polymerizing mixtures of the nanoparticles and monomer solutions. The swelling response of these composite systems to different crosslinking molecular weights, temperature, and the effect of the presence of the magnetic nanoparticles were examined.