Malignant tumors are one of the main causes of death in Poland. One of the objectives of contemporary biomedical research is to maximize the effects of therapeutic strategies. The actions undertaken to improve therapeutic agents are aimed at reducing the side effects of cancer treatments. Another direction of investigations is the search for protective substances that reduce the toxicity of the drug to normal cells. Carbon-based nanomaterials (fullerenes and their derivatives, graphene, carbon nanotubes, nanodiamonds) are a broad class of nanoparticles that have potential biomedical applications in both therapy and diagnostics. The aim of this paper is to review biological properties of fullerenols in the context of their use in various strategies of cancer treatments. The authors also discuss the possibility of simultaneous use of nanoparticles in therapy and diagnosis, that is, in theranostics. Current knowledge indicates that fullerenes and their hydrophilic derivatives, especially fullerenols, show low or no toxicity. They may contribute to the inhibition of tumor growth and protection of normal cells through their antioxidant properties, as well as to the regulation of expression of genes involved in apoptosis and angiogenesis, and stimulation of the immune response. Gadoliniumcontaining endohedral fullerenes are less toxic as a contrast agents in magnetic resonance imaging, and they may also inhibit tumor growth, which is a promising result for theranostics.