Abstract A new microcrystalline compound Al 6O 4(OH) 10(leucine) 2·5H 2O of possible biological and biochemical interest has been prepared and characterized by chemical analysis, i.r. spectrum, X-ray diffraction and thermogravimetric analysis. It was exposed to γ-irradiation at 77 K and at room temperature. Paramagnetic species formed were studied by ESR spectroscopy. The leucine radical has been identified which seems to be stabilized in the aluminium leucine compound by crystalline water. Coordinated leucine molecule in aluminium hydroxide acts as a trap for γ-irradiation energy.