We previously established that Multifrequency Electromagnetic Pulse (MEMP) treatment selectively eradicates tumorigenic cells in vitro. While this treatment proved safe in mice and prevented tumor formation by pre-treated cells, its efficacy against established tumors remained unknown. Here we evaluate the therapeutic effect of two different systemic MEMP treatment regimens (30 Hz, >2 T) on syngeneic MC38 colon adenocarcinoma es-tablished subcutaneously in C57BL/6 mice. The impact of MEMP on anti-tumor immune infiltration (CD4, CD8, CD68) responses, as well as oxidative stress (HO-1, MDA), and DNA damage (γH2AX), cell biology markers, were analyzed by immunohistochemistry. The MEMP regimes significantly reduced the growth of the xenografted tumors leading to an apparent regression in a small subset of animals, and extended survival without af-fecting animal welfare. Of note, mice that achieved complete tumor regression mounted a protective immune response, demonstrating robust resistance to a subsequent tumor re-challenge, indicative of immunological memory. Importantly, the quantitative penetra-tion of immune effectors CD68+ cells into tumors suggests the involvement of a strong, macrophage-mediated anti-tumor response, although the ultimate mechanisms driving the MEMP effects in vivo deserve further research. These findings place MEMP as a prom-ising anti-cancer treatment and a strong candidate procedure for combination with other systemic immunotherapies.