Introduction. For the treatment of primary inoperable and metastatic solid human tumors with local regional arterial blood flow, a minimally invasive embolization method is used, which causes a decrease in the growth rate and size of the malignancy (cytoreduction), local side effects of which depend on the viscosity of the embolizing agent. Nanostructured ferro- and ferrimagnetics (ferrites) allow selectively achieving not only cytoreduction, but also full effect by following the embolization of magnetic hyperthermia (MHT). Material and methods. The study of a new original embolizing nano-ferrimagnetic nanoembosil with low viscosity was performed with intra-arterial (i.a.) administration to anesthetized animals with intramuscular (i.m.) developed tumors (PC1 and VX2). This allowed us to evaluate its effectiveness using adequate criteria and the method of variation statistics (Fisher-Student’s criterion «t» in the environment of the IBM SPSS 21 package) and statistically significant differences at p≤0.05. Results and discussion. It is shown that nanoembosil in doses of 0.1 and 0.2 ml for rats and 1.5 ml for rabbits is dose-dependent, and in the case of VX2 it is statistically significant (p=0.001) for a long time in 2-6 times inhibits the rate of tumor growth without side effects with long-term stabilization and cytoreduction by 50-65%. Structural analogs of nanoembosil in the practice of medicine there. Conclusion. Thus, nanoembosil can be considered an original effective agent for selective arterial embolization and it is recommended to continue its preclinical study in therapeutic and preoperative modes. Good tolerance of i.a. administration of nanoembosil in the studied doses with no local side effects opens the possibility of studying the possibility of studying it as a thermo-sensitive nanomaterial for low-frequency MHT.