Objective: Many reports have shown that the prognostic nutritional index (PNI) is associated with the clinical outcomes of patients with biliary tract cancer (BTC), with the results being inconsistent. We therefore comprehensively evaluated the prognostic significance of the PNI in BTC by performing a meta-analysis. Methods: We identified relevant studies by searching PubMed, Embase, Web of Science and, the Cochrane Library. The combined hazard ratio (HR) and odds ratio (OR) with 95% confidence interval (CI) were used to evaluate the association between PNI and overall survival (OS) and the clinical characteristics of BTC. Results: We included seven studies with 1608 patients in this meta-analysis. The pretreatment low PNI correlated significantly with worse OS (HR = 1.65, 95%CI = 1.42-1.93, p < 0.001). In addition, the prognostic effect of PNI are reliable in different subgroups of ethnicity, sample size, histology, treatment, PNI cutoff, and cutoff determination. The low PNI was also related to poor differentiation (OR = 1.95, 95%CI = 1.34-2.85, p = 0.001) as well as higher T stage (OR = 2.51, 95%CI = 1.69-3.74, p < 0.001) in BTC. Conclusion: The low PNI is significantly associated with inferior prognosis of patients with BTC and aggressive clinical factors. The PNI could be applied as an independent prognostic marker for patients with BTC.