Statement of Problem: Oral Lichen Planus (OLP) is a common chronic inflam-matory mucocutaneous disease and has different types. If they are symptomatic, they must be treated. Corticosteroid, especially in topical form, is commonly used.Purpose: The purpose of this study was to compare the therapeutic effects of two corticosteroid mouthwashes on treatment of symptomatic OLP.Materials and Method: The participants of this single-blind study were 44 symptomatic OLP patients. They included 27 females and 17 males. They were randomly divided into two groups and were given drug A (Dexamethasone 0.1%) or B (Triamcinolone acetonide 0.2%) for four weeks. Extension of lesions (mm2) and severity of symptoms (based on Visual Analogue Scale) were recorded before and after treatment (weeks 1, 2, 4). Finally, SPSS 12 was used and Man-Whitney test was run to analyze the data.Results: In both groups extension of lesions and burning sensation decreased significantly during the four weeks of treatment. There was no statistically significant difference between the two groups. However, Dexamethasone 0.1% was more efficacious, in the fourth week, in reducing the size of lesions than Triamcinolone acetonide 0.2% ( p = 0.02).Conclusion: Both mouth washes were useful in diminishing pain and decreasing the size of lesions. However, Dexamethasone 0.1% was recommended for treat-ment of OLP because it was more efficacious than Triamcinolone acetonide 0.2%.