Superparamagnetic gels based on polyacrylamide and magnetite were synthesized by the in situ preparation of magnetite nanoparticles in polyacrylamide (PAM) physical hydrogels at different polymer concentrations. The formation of magnetite nanoparticles and their magnetic properties were characterized by Fourier transform infrared (FTIR) spectroscopy, rheometry, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). FTIR spectroscopy showed that all composite gels had features related to pure PAM. The structural characterization by Rietveld method revealed an average crystallite size below 18 nm and SEM micrographs of the gel with Fe₃O₄ showed that the particles have spherical structures. The rheology-related measurements indicated that the gels had a strong pseudoplastic character. Magnetic measurements confirmed the superparamagnetic behavior of the obtained magnetite nanoparticles, both in the form of pure powder and within PAM gel matrix. Magnetite crystallite size decreased as PAM content was increased, which was explained as a function of thermodynamic and kinetic effects.