Mucus of cystic fibrosis patients exhibits altered biochemical composition and biophysical behavior, but the causal relationships between altered CFTR function and the abnormal mucus seen in various organ systems remain unclear. We used cultured gallbladder epithelial cells (GBEC) from wildtype and Cftr^(-/-) mice to investigate mucin gene and protein expression, kinetics of post-exocytotic mucous granule content expansion, and biochemical and ionic compositions of secreted mucins. Muc1, Muc3, Muc4, Muc5ac and Muc5b mRNA levels were significantly lower in Cftr ^(-/-) GBEC compared to wildtype cells, whereas Muc2 mRNA levels were higher in Cftr ^(-/-) cells. Quantitative immunoblotting demonstrated a trend toward lower MUC1, MUC2, MUC3, MUC5AC and MUC5B mucin levels in Cftr ^(-/-) cells compared to cells from wildtype mice. In contrast, the levels of secreted MUC1, MUC3, MUC5B and MUC6 mucins were significantly higher from Cftr ^(-/-) cells; a trend toward higher levels of secreted MUC2 and MUC5AC was also noted from Cftr ^(-/-) cells. Cftr ^(-/-) cells demonstrated slower post-exocytotic mucous granule content expansion. Calcium concentration was significantly elevated in the mucous gel secreted by Cftr ^(-/-) cells compared to wildtype cells. Secreted mucins from Cftr ^(-/-) cells contained higher sulfate concentrations. Thus, absence of CFTR is associated with pleiotropic effects on mucins in murine GBEC.