A chemical etchant for UO2consisting of three parts concentrated HCl and one part concentrated HNO3is reported. This etchant, when used for ten minutes at 60°C on cleaved {111} surfaces, produces distinctive pits at dislocations intersecting the surface and at low-angle grain boundaries. The fact that the etch pits mark the sites of dislocations was shown by comparing the enlargement of pits with etching time and the etch pits on matching cleavage faces. Comparison of etch rates at various temperatures gave an activation energy of 15.1 kcal/mole.