ObJECTIVE:Understand the change and damage of rats and mice buccal mucosa tissue structure posioned by acrylonitrile and alcohol. METHODS: Using optical microscope and transmitted electron microscope (TEM) techniques, observed the structure of rats and mice buccal mucosa which posioned by acrylonitrile and alcohol for 13 weeks in different dosages. RESULTS: Acrylonitrile can damage the ultrastructure of the cells and lead to precancerous dysplasia,such as enlargement and deformation of nuclei, reducing of desmosomes and hemidesmosomes,break of basement membrane,swelling and denaturalization of mitochondrion. The degree of damage was correlated with its dosage. Alcohol can increase the damage caused by acrylonitrile. CONCLUSION: Both acrylonitrile and alcohol can destroy the ultrastructure of cells,TEM is helpful for diagnosing disease in their early stage,and buccal mucosa can be used as a window for observing the disease caused by many toxic factors.