Nanocomposite hydrogels of sodium alginate (SA) / polyacrylamide (PAM)/ graphene oxide (GO) were prepared by in situ polymerization.The structure and properties of hydrogels were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscope (AFM), Fourier transform infrared spectroscopy(FTIR) and thermogravimetric analysis (TG). The effect of GO content on the chemical structure, mechanical and swelling properties of the hydrogels was investigated. The results show that the well exfoliated GO flakes could be uniformly dispersed in the polymer matrix, therewith the intermolecular interactions between the components might be enhanced and parts of PAM macromolecules chains were probably grafted onto the GO nanosheets, which in turn changed the microstructure of the hydrogels and resulted in significant enhancement of mechanical properties of the composite hydrogels. As a result, in comparison with the two hydrogeles of pure SA and pure PAM, the prepared composite hydrogels exhibited both of higher tensile strength and breaking elongation up to 200%, as well as a higher compressive strength up to 156%. The swelling capacity of the composite hydrogels increased and then declined with the increasing GO content, while increased with the increasing SA content.