Cyclodextrins and their derivatives are widely used as drug delivery agents due to their ability to hold small molecules in their internal cavity. Reduction of toxicity by cyclodextrins is proven in the case of non-invasive or oral delivery of drugs, but the authors disagree on the intravenous use of these substances. In this paper, we compare two substances-the cluster complex of niobium [Nb6Cl12(H2O)6]2+ for which we previously showed anticancer activity, and its conjugate with cyclodextrin [Nb6Cl12(H2O)6]2+@\gamma-CD. To assess the effect of cyclodextrin on the toxicity of the solution, we intravenously administered a wide range of doses of two substances to BALB/C mice. After assessment of acute toxicity, the study of organ morphology was carried out. The results showed that conjugation with cyclodextrin not only did not reduce the toxicity of the cluster complex, but also increased it, causing vascular disorders in several organs.