Stimulus-responsive drug delivery systems have been widely used for many biomedical applications. Magnetic stimulation may serve as an important external stimulus for drug delivery. In this study, we hypothesized that the on-demand release of anticancer drugs could be achieved with a macroporous alginate ferrogel under the influence of magnetic stimulation to enhance therapeutic efficacy in a tumor-bearing mouse model. A ferrogel containing alginate, iron oxide nanoparticle, and gelatin particle was prepared by ionic crosslinking with calcium ions and dissolving the gelatin particle at 37 °C. We investigated the influence of porosity on the degree of deformation of alginate ferrogel and evaluated the release behavior of doxorubicin (DOX) by applying magnetic field to the ferrogel. In vitro viability of cancer cells cultured with DOX-releasing macroporous alginate ferrogel after magnetic stimulation was greatly decreased compared to that of cells cultured with alginate ferrogel. The therapeutic efficacy of DOX-releasing macroporous alginate ferrogel also increased in tumor-bearing mice following magnetic stimulation. Thus, this approach to design a ferrogel responsive to magnetic stimulation may prove useful for the development of smart drug delivery systems.