Percutaneous liver biopsy is the standard method for histological diagnosis of diffuse liver diseases; however, endoscopic ultrasound-guided tissue acquisition (EUS-TA) has recently emerged as an alternative. We report a case of autoimmune hepatitis (AIH) diagnosed using EUS-TA with the wet-suction technique. A woman in her 40s presented with fatigue and jaundice. Laboratory tests showed severe liver dysfunction (total bilirubin 5.7 mg/dL, AST 1006 U/L, ALT 1639 U/L), positive antinuclear antibody (1:640), and mildly elevated IgG (1802 mg/dL), while viral hepatitis markers were negative. EUS-TA was performed using a 19-gauge FNB needle primed with heparinized saline. The left hepatic lobe was punctured transgastrically with 20-mL suction and approximately 10 strokes. A specimen with a maximum core length of 11 mm containing four portal tracts was obtained. Histopathology showed interface hepatitis consistent with AIH. No adverse events occurred. Steroid therapy led to rapid improvement in liver function. Wet-suction EUS-TA may be a useful method for obtaining adequate tissue for the diagnosis of diffuse liver diseases.