Assessing small intestinal mucosal injuries in patients with cirrhosis is crucial. Here, we measured intestinal fatty acid-binding protein (I-FABP) levels, a useful marker of small intestinal mucosal injury, in patients with cirrhosis to determine their relationship with liver function and complications. The study included 71 patients with cirrhosis admitted for treatment of cirrhotic complications or hepatocellular carcinoma (cohort A, derivation cohort) and 104 patients with cirrhosis who received direct-acting antiviral therapy for HCV (cohort B, validation cohort). I-FABP levels measured by ELISA were evaluated relative to hepatic reserve and compared with non-invasive scoring systems for diagnostic performance in cirrhotic complications. In Cohort A, the median I-FABP level was 2.80 ng/mL, which was significantly elevated in patients with reduced hepatic reserve (CTP grade A/BC: 2.33/3.17 ng/mL, p = 0.032) and complications with gastroesophageal varices (GEV) ((-)/(+): 1.66/3.67 ng/mL, p < 0.001). Multiple logistic regression analysis identified I-FABP as the only factor contributing to the presence of GEV (OR; 3.278, p = 0.005), which outperformed noninvasive scoring systems for GEV diagnosis (sensitivity 84.6%; specificity 84.2%). Cohort B confirmed these findings with higher I-FABP levels in patients with reduced hepatic reserve (CTP grade A/BC: 2.46/3.64 ng/mL, p = 0.008); I-FABP was the only factor contributing to the presence of GEV (OR; 1.433, p = 0.028) with the highest discriminative ability (sensitivity 69.6%; specificity 63.8%). In conclusion, elevated small-intestinal mucosal injury in patients with cirrhosis was linked to reduced hepatic reserve and GEV. I-FABP levels may reflect portal hypertension and be useful for management of patients with cirrhosis.