•Fe3O4 nanoparticles were synthesized in situ in polyacrylamide/chitosan hydrogels.•Magnetic hydrogels can adsorb methylene blue with a high adsorption capacity of 1603 mg/g.•Kinetics and isotherm models of adsorption process can be better described.•Adsorption mechanism is mainly based on electrostatic attraction. In this study, Fe3O4 magnetic nanoparticles were synthesized in situ in the polyacrylamide/chitosan (PAAm/CS) hydrogel networks. The obtained hydrogels are characterized by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The results confirm that the three-dimensional network structure of the hydrogels is incorporated with Fe3O4 nanoparticles. The adsorption properties of PAAm/CS/Fe3O4 hydrogels for methylene blue (MB) in aqueous solution were studied using Ultraviolet and visible spectrophotometry (UV–vis). The results show that when compared to PAAm/CS hydrogels, PAAm/CS/Fe3O4 hydrogels can adsorb MB with higher adsorption capacities of approximately 1603 mg/g, and the kinetics and isotherm models of the adsorption process could be better described by the pseudo-first order model and Langmuir isotherm model, respectively. Due to the facile preparation, high adsorption capacity, and low cost, the PAAm/CS/Fe3O4 hydrogels are good adsorbents for MB and exhibit significant potential in the treatment of sewage.