The right nutrition is an important part of a healthy life. During the diagnosis and treatment, the nutrition insufficiency develops in the 40 % of the cancer patients, and malnutrition is the common complication with 20 – 80 % ratio. The factors that cause nutrition deficiency at the oncology patients depend on tumor, the treatment, the side effects of the treatment and the metabolic status. The objective of the nutrition supplement is to preserve the weight of the patient, to prevent the failure of the general status and the development of the malnutrition. General status, the degree of malnutrition, stage of cancer, side effects due to the treatment must be taken into consideration when oral, enteral or parenteral nutrition supply are chosen. This article has been written to guide the medical professionals who care oncology patients with nutrition deficiency.