In order to study the toxic consequences of arsenic at different levels on hippocampal neurons of rat, different doses of sodium arsenite (0, 0.08, 0.40, 2.00 and 10.00 mg/L) were given to observe the changes of viability, morphological and biochemical parameters. The results showed that the arsenite content in primarily cultured rat hippocampal neurons decreased in growth of viable cells. The morphometric analysis showed that the isolated neonatal hippocampal neurons exposed to lower concentration of arsenic had cytoplasm vacuoles, frothing and nuclear condensation with the intact membrane, indicating the possible induction of apoptosis, whereas higher dose of arsenic leaded to the appearance of necrosis. The degeneration of cytoplasm with the appearance of large vacuoles and loss of cell-cell junction were also observed. Meanwhile the Nissles decreased in the cytoplasm confirmed by the Tolidine blue. Biochemically determined increase in the viability of L-LDH showed increased in extra-cellular release as well as decrease in AchE. Some results showed the dose-time dependent relationship. It is suggested that the neonatal hippocampal neurons of rat treated with different doses of arsenic suffered from morphological changes including degeneration, apoptosis and necrosis in various degrees.