Reduced graphene oxide (RGO)–gelatin nanocomposite hydrogels were prepared via a facile one-pot synthesis by heating the mixture of an aqueous graphene oxide (GO) suspension and a gelatin solution at the desired ratio at 95 °C for 24 h. The hydrogels were formed mainly by chemically cross-linking gelatin macromolecular chains with graphene nanosheets where gelatin acts as a reducing agent to convert GO to RGO and was chemically grafted onto the graphene surface. Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction and scanning electron microscopy were employed to characterize the RGO–gelatin nanocomposite hydrogels. Rheological tests showed that the storage modulus of the hydrogels was up to 172.3 kPa. Water swelling tests found that the swelling behavior of the dried hydrogels followed Fick's diffusion law, with an equilibrium swelling ratio of up to 44.7. The enzymatic degradation tests demonstrated that the hydrogels lost up to 29% of their original weight after degradation for 24 h. The relatively high mechanical properties and biodegradability could provide RGO–gelatin hydrogels potential in tissue engineering and drug delivery.