This study was designed to investigate the qualitative and quantitative changes in brain tissue following aluminum chloride (AlCl3) administration and to determine whether boric acid (BA) has a protective effect against brain damage induced by AlCl3. For this aim, Sprague-Dawley rats were randomly separated into eight groups: (1) control, (2) AlCl3 (5 mg/kg/day), (3, 4 and 5) BA (3.25, 36 and 58.5 mg/kg/day), (6, 7 and 8) AlCl3 (5 mg/kg/day) plus BA (3.25, 36 and 58.5 mg/kg/day). After the animals were killed, the total numbers of neuron in the brain of all groups were determined using an unbiased stereological analysis. In addition to the stereological analysis, all brains were examined histopathologically by using light and electron microscopy. The stereological and histopathological results indicated a high damage of the rat brain tissues in the AlCl3 and AlCl3 + high dose BA (36 and 58.5) treatment groups. However, protective effects on neuron were observed in the AlCl3 + low dose BA (3.25) group when compared other AlCl3 groups. Our stereological and histopathological findings show that low-dose BA, as a proteasome inhibitor, can decrease the adverse effects of AlCl3 on the cerebral cortex.