Magnetic-mediated hyperthermia (MMT) is emerging as one of the promising techniques, which could synergistically treat cancer along with current treatment techniques such as chemotherapy and radiotherapy and trigger on-demand release of therapeutic macromolecules. However, the low specific absorption rate and potential in vivo toxicity of magnetic nanomaterials as the MMT mediators restrict the new advancements in MMT treatment. Herein, for the first trial, the unique inductive heating property of hypertonic saline (HTS), a clinically applied solution exhibiting several physiological effects under alternative magnetic field (AMF), was systematically investigated. Though without magnetic property, due to the dipolar polarization under the electromagnetic radiation, HTS can induce enough high and rapid temperature increase upon exposure under AMF. Based on such an observation, PEG-based HTS hydrogel was fabricated for the inhibition of unwanted diffusion of ions so as to ensure the ideal temperature rise at the targeted region for a longer time. Furthermore, an anticancer drug (doxorubicin) was also incorporated into the hydrogel to achieve the magnetic field/pH stimuli-responsive drug-sustainable release as well as synergistic thermochemotherapy. The potential application of the drug-loaded HTS-PEG-injectable hydrogel for breast cancer postsurgical recurrence prevention is demonstrated. Significant in vivo suppression of two kinds of breast cancer models was achieved by the hybrid hydrogel system. This work explores a new biomedical use of clinical HTS and a promising cancer treatment protocol based on HTS-PEG hydrogel for magnetic hyperthermia combined with stimuli-responsive chemotherapy for breast cancer postsurgical recurrence prevention.