Quantum chemical investigation using density functional theory (DFT) approach is performed to assess the interactions of the anticancer 5‐fluorouracil (FU) drug and B36N36 nanocluster. The alkali (AMs) and alkaline earth (AEMs) metals encapsulated B36N36 nanoclusters are also considered for FU adsorption. Results indicate the significant interaction of FU drug with pristine as well as encapsulated boron‐nitride nanoclusters. Accordingly, the electronic structure of the nanoclusters is very sensitive to the FU adsorption. The resulting complexes have less energy gap than the bare ones, which can produce an appropriate signal for detection of the FU drug. Adsorption of six FU molecules on the top of each nanocluster indicates their high capacity for FU drug loading. The FU molecules also interact effectively with the AMs and AEMs encapsulated nanoclusters in the aqueous medium, which facilitates the drug delivery. The studied complexes have higher dipole moments in aqueous phase than in vacuum medium. The pristine and encapsulated B36N36 nanoclusters are suggested as prospective novel delivery agents and detectors for FU drug thanks of their suitable features.