Statement of problem: Salivary gland tumors comprises a large groupe of oral cavity lesions. Ductal and myoepithelial cells are introduced as original cells in salivary gland tumors .The histogenesis of salivary gland tumors are controversial.Purpose: With considering the role of s-100 protein in demonstration of myoepithelial cells, the purpose of this study was the determination of immunoreactivity pattern and distribution of myoepithelial cells in PA, ACC and MEC.Materials and method: Formalin- fixed paraffin- embedded from 5 PAs, 5 ACCs and 5 MECs were studied immunohistochemically with employing S-100 protein.The S-100 protein positive cells were counted and mean score of Labeling Index (LI) were achieved. The immunoreactivity and staining pattern of each tumor were stablished .Lack of bleeding and necrosis was considered as inclusion criteria.Result: 1) In PA:  The plasmacytoid and some of ductal cells were stained positive (LI=0.34).The immunostaining reaction was moderate to severe.2) In ACC: S-100 protein Immunoreactivity was negative (LI=0).3) In MEC:  The small numbers of epithelial cells were stained. Since, the stained epithelial cells was lesser than 5%, the MECs was considered negative.Conclusion: Based on this study, the myoepithelial cells do not comprises the main cellular part in ACC and MEC.Keywords: S-100- Pleomorphic adenoma- Adenoid cystic carcinoma- Mucoepidermoid carcinoma- Immunohistochemical study