Some V complexes are considered as promising antidiabetics. These compounds are able to mimic most of the biological effects of insulin in different organisms. Diacetylacetonateoxovanadium(IV) [V^IVO(acac)₂] decreases glucose concentration in blood and enhances the kinase activity of the insulin receptor in cells more than other V compounds. Proteins play a major role in the definition of the mechanism of action of metallodrugs because of their high concentration in biological fluids and their high affinity for metal ions. To better understand the mechanism of action of [V^IVO(acac)₂] it is important to define its reaction with proteins. Here, we report the structures obtained upon reaction of [V^IVO(acac)₂] with the model protein lysozyme. The crystallographic study reveals the loss of the ligands, the oxidation of V^IV to V^V, and the subsequent formation of fascinating adducts of the protein with different polyoxidovanadates (POVs). POVs constitute a sub-class of the vast polyoxidometalates (POMs) family that exerts various biological activities, such as anti-Alzheimer's disease, antibacterial, anti-cancer, anti-diabetes, anti-virus, and so on. The obtained structural data expand the repertoire of structures of known protein-POM complexes and provide useful information on the recognition of POVs by proteins.