B cell lymphoma 6 (BCL6) is a protein that is vital for lymphogenesis. Its expression has been well established in lymphoma, especially in diffuse large B-cell lymphoma. Its role in carcinogenesis is less well understood. Previous study shows that BCL6 expression may regulate p19 functions, an important regulator for the p53 pathway. No prior study has attempted to evaluate the significance of BCL6 and p19(ARF) expression in a large cohort of patients with gallbladder carcinomas (GBCs). We selected 164 patients with GBC and performed immunostains for BCL6 and p19(ARF). BCL6 expression and p19(ARF) expression were evaluated using a histochemical score (H-score). We then correlated the results with various clinicopathological factors, disease-specific survival (DSS), and disease-free survival (DFS). BCL6 overexpression was significantly associated with high pT status, high TNM stage, higher histological grade (p = 0.029), vascular invasion, perineurial invasion, high Ki-67 labeling index, and low p19 expression. Importantly, BCL6 overexpression in GBC was strongly associated with worse DSS (p < 0.0001) and DFS (p < 0.0001) in the univariate analysis, and remained independently predictive of adverse outcomes (p = 0.001, hazard ratio (H.R.) = 3.098 for DSS; p = 0.002, H.R. = 2.255 for DFS). Low p19(ARF) expression was correlated with a poor DSS (p = 0.0144) and DFS (p = 0.0032) in the univariate analysis but was not prognosticatory in the multivariate analysis. In GBC, BCL6 overexpression correlated with adverse phenotypes and decreased p19(ARF) expression. BCL6 overexpression also independently predicts worse DSS and DFS, suggesting it has a role in tumorigenesis or carcinogenesis and could be a potential prognostic indicator in GBC.