Despite the progress of medicine, malignant tumors are still one of the leading health problems of the modern age. The use of current treatment modalities for malignant tumors still does not produce the desired results in a large number of cases. The development of science and the discovery of new technologies such as nanotechnology open up new possibilities in tumor therapy. Nanotechnology is a science whose foundations are based on the fact that particles in nano dimensions are subject to the laws of quantum mechanics and exhibit different properties in contrast to particles on a macro scale. Thanks to their specific behavior, they have a potential place in the diagnosis and therapy of malignant tumors, that is, they show promising possibilities in molecular diagnostics, as contrast agents in imaging diagnostics, then in the delivery of antitumor drugs to target sites in the body, and in photothermal, magnetothermal and gene therapy. Given that nanotechnology is a relatively young field in medicine, the possibilities of applying nanoparticles in the mentioned discipline and their impact on biological systems have not been sufficiently explored. In addition to knowing the basics of nanoparticles, it is important to know their behavior within the biological system so that they can be used for diagnostic and therapeutic purposes in humans. The aim of this paper is to gain a critical insight into nanotechnology through the basics of nanotechnology, its diverse use in oncology, the advantages of nanotechnology and potential obstacles in its application to patients.