Blue nevus may rarely appear in a plaque form. Because of its rarity and unusual appearance, this nevus may present a diagnostic problem and gives no definite prognosis. We report a case of plaque-type blue nevus in a 25-year-old man. He presented an irregularly demarcated plaque, measuring 1.5×3cm, composed of multiple grouped slate gray to blue papules of varying size with intervening faint gray-blue discoloration on the back, which had existed for 10 years. Histopathological examination showed clumps of numerous heavily melanin-laden dendritic melanocytes in the reticular dermis with intervening stromal fibrosis. Numerous melanophages were intermingled with the melanocytes. There were no islands of pale cells seen in the cellular blue nevus and no malignant changes such as nuclear and cytoplasmic pleomorphism, mitotic figures and so on. The diagnosis of plaque-type blue nevus was made and its histopathological features were consistent with a common blue nevus.