Nucleus plasma ratio was measured and silver-binding nucleolar organizer (AgNORs) were counted in 31 cases of cholangiocarinoma (11 cases were well-differentiated, 10 case moderately differentiated and 10 cases poorly differentiated) and in 17 cases of atypical epithelial hyperplasia related to hepatolithiasis (9 cases were simple hyperplasia, 8 cases atypical epithelial hyperplasia) by AgNORs techique and image analysis.The results showed that mucleus plasma ratio and AgNORs counts increased significantly from well-differentiated to poorly differentiated cholangiocarcinoma (Ｐ＜0.01). No statistically significant differance was shown between nucleus plasma ratio of atypical hyperplasia and well-differentiated cholangiocarinoma.The data imply that chronic proliferative cholngitis in the presence of hepatolithiasis can progress to atypical epithelial hyperplasia which may be an important precursor of cholangiocarcinoma.