We have investigated the effects of sodium azide, a specific inhibitor of cytochrome c oxidase (COX), on the microtubule morphology and cell viability of nerve cells. Human neuroblastoma SH-SY5Y cells were exposed to sodium azide to check mitochondrial complex IV activity by microassay method, cell viability by MTT method and microtubules by confocal microscopy and image analyzer. Exposed to 16-64 mmol/L sodium azide for 1 hour, the mitochondrial complex IV activity decreased dose-dependently. MTT assay showed a dose- and time- dependent decrease of cultured nerve cells which were treated with 16-128 mmol/L sodium azide for 1-8 hours. Exposed to 64 mmol/L sodium azide for 4 hours, the processes of cells were shortened, almost disappeared, cell bodies became round and bright under contrast microscope. Meanwhile, microtubles were disassembled and became disorderly, the content and distribution of tubulin (microtubule protein) were reduced, expecially in the processes. It is indicated that sodium azide inhibits the assembly and polymerization of tubulin in microtubules. The damage of axons induced by microtubule collapse further blocks the intercellular signal transduction and intracellular material transportation which are essential to a cell.