OBJECTIVE To determine the expression and clinical significance of Fas and FasL in cases of occurrence and development of pleomorphic adenoma and adenoid cystic carcinoma(ACC) in parotid gland. METHODS Using Immunohistochemistry techniques and quantitative analysis under computerized system, we investigated Fas-FasL expression in 21 cases of normal parotid gland, 35 cases of pleomorphic adenoma in parotid gland and 32 cases of ACC in parotid gland. RESULTS All cases of ACC of parotid gland showed Fas and FasL negative expression, no correlation was found between the expression of Fas-FasL and the histological type and the pathological grades of ACC. Although both normal parotid gland and pleomorphic adenoma of parotid gland had distinct expression of Fas and FasL, the positive expression of Fas FasL in pleomorphic adenoma of parotid gland cases were both significantly lowered (P<0.01) than that in normal parotid gland. CONCLUSION Expression of Fas-FasL and Fas FasL mediated cell apoptosis disturbance had significant correlations with the occurrence and malignant development of pleomorphic adenoma and ACC in parotid gland.