The cytotoxic effect of nitric oxide on primarily cultured rat cerebellar granule cells was stuatea, and the mechanisms were discussed. The results showed that nitric oxide donor S-nitroso-N-acetyl-penicillamine (SNAP; 500 (imol/L) could induce apoptosis in immature cultures of cerebellar granule cells. Flow cytometry and HPLC analyses revealed that after treatment with SNAP, the mitochondrial transmembrane potential and the cellular ATP content decreased significantly. Nitric oxide scavenger hemoglobin could effectively prevent the neuronal mitochondria from dysfunction and attenuate apoptosis. The results suggested that nitric oxide activated the apoptotic program by inhibiting the activity of mitochondrial respiratory chain and thus decreasing the cellular ATP content. The cytotoxic effect of nitric oxide on pre-cultured rat cerebellar granule cells was stuatea, and the mechanisms were discussed. The results showed that nitric oxide donor S-nitroso-N- acetyl-penicillamine (SNAP; 500 (imol / L) in immature cultures of cerebellar granule cells. Flow cytometry and HPLC analyzes revealed that after treatment with SNAP, the mitochondrial transmembrane potential and the cellular ATP content decreased significantly. Nitric oxide scavenger hemoglobin could effectively prevent the neuronal mitochondria from dysfunction and attenuate apoptosis. suggested that nitric oxide activated the apoptotic program by inhibiting the activity of mitochondrial respiratory chain and thereby decreasing the cellular ATP content.