We examined the expression of MUC1, MUC2, MUC5AC, and MUC6 by immunohistochemical staining in atypical adenomatous hyperplasia (AAH), bronchioloalveolar carcinoma (BAC), and adenocarcinoma with mixed subtypes (MX) to study the association between the biologic features of adenocarcinoma of the lung and mucin expression. MUC1 expression was decreased significantly in the progression from AAH through BAC to MX, while the levels of expression of MUC2, MUC5AC, MUC6, and depolarized MUC1 were increased significantly. Alterations in the expression of depolarized MUC1, MUC5AC, and MUC6 were correlated significantly with p53 gene abnormalities. Depolarized MUC1 expression also was correlated significantly with Ki-67 expression, and down-regulation of MUC1 expression and up-regulation of MUC6 expression were correlated significantly with tumor size. Our results suggest that the expression of these mucins might be associated with the progression of adenocarcinoma of the lung.