Nanoparticles create exciting platforms for anticancer immunotherapy and vaccination, though their inherent immunomodulatory properties have remained underexploited. Ammonio methacrylate copolymers (AMC) are well-established excipients in pharmaceutical industry and components of controlled-release oral formulations. Here, we demonstrate that nanoscaling of type A and B AMC (Eudragit RL and RS) endows these inactive ingredients immunostimulatory properties exploitable for cancer therapy. The particles induce the secretion of various pro-inflammatory cytokines and chemokines from the cells of innate immunity. Though the underlying mechanisms are not fully uncovered, the current work established the partial involvement of Toll-like Receptor 4 (TLR4) and Nuclear factor κB (NF-κB). The size and charge-dependency of the particles' pro-inflammatory properties and cytokine/chemokine induction profile was also demonstrated. Within the context of cancer immunotherapy, biweekly peritumoral nanoparticle injection led to a complete regression of the syngeneic colorectal tumor, or a significant growth retardation thereof, considerably extending the survival of tumor-bearing animals. Additionally, presence of the immunological memory in treated animals was established. Given their better economical and relatively safer profile compared to well-established chemo- and immunotheraputics, and their ability to serve as carriers for drug targeting, vaccination and combination therapy, AMC nanoparticles (AMCNP) are fascinating subjects for further research in the field of cancer therapy.