Background and Objectives: The geriatric nutritional risk index (GNRI) is an easily calculable index that can be determined using three common clinical variables. The GNRI is suggested to be related to sarcopenia in cirrhotic patients. However, the relationship between the GNRI and the prognosis in patients with liver cirrhosis (LC) has not been reported. The aim of the present research is to study the association of the GNRI with the nutritional status, hepatic function reserve, and prognosis in patients with liver cirrhosis (LC). Materials and Methods: A total of 370 cirrhotic patients whose nutritional statuses were evaluated using anthropometric measurements and bioimpedance analysis were studied. The associations between the GNRI and nutritional status and the GNRI and hepatic function reserve were analyzed. We also investigated the GNRI and prognosis of patients with LC. Results: The median age of the enrolled patients was 66 years old, and 266 (71.9%) patients had viral hepatitis-related LC. The GNRI was shown to decrease with the progression of chronic liver disease, represented by an increased FIB-4 index and severe Child-Pugh and mALBI grades. In addition, a low GNRI (<92) was associated with severe cirrhosis-related metabolic disorders, including a low branched-chain amino acid-to-tyrosine ratio (BTR) and a low zinc value. The GNRI was positively correlated with two nutrition-related anthropometric variables (% arm circumference and % arm muscle circumference), and a low GNRI was related to a low skeletal muscle mass index (SMI) (<7.0 kg/m2 for men or <5.7 kg/m2 for women), as determined by using bioimpedance analysis. In addition, patients with a low GNRI (<92) had a poorer prognosis than those with a high GNRI (≥92) (log-rank test: p = 0.0161, and generalized Wilcoxon test, p = 0.01261). Conclusions: Our results suggest that a low GNRI is related to severe chronic liver disease, low muscle volume, and a poor prognosis of patients with cirrhosis.