Treatment of oncological diseases using Boron Neutron Capture Therapy (BNCT) is an important issue of our time. Cancer cells accumulate a boron-containing drug, after which they are irradiated with a beam of epithermal neutrons, a nuclear reaction 10B(n,α)7Li occurs, and the products of a nuclear reaction destroy these cells. In BNCT, it is generally accepted that the total dose of ionizing radiation consists of four components: boron dose, dose from fast neutrons, dose from thermal neutrons, and dose of gamma radiation. Dose values and their ratio strongly depend on the neutron flux; therefore, the measurement of the neutron flux (yield) is an urgent task. In this work, the neutron yield was measured by the activation of the target with the radioactive isotope beryllium-7, which is formed in the reaction of neutron generation 7Li(p,n)7Be. It was found that the neutron yield from a specifically manufactured lithium target is in good agreement with the calculated one, which is important for planning therapy.