Abstract： AIM: To explore the clinic value of fatty renal capsule thickness in diagnosis of fatty liver disease. METHODS: Thirty cases with mild and or with moderate to severe degree of fatty liver were collected, and their fatty renal capsule thickness was measured. RESULTS: The fatty renal capsule thickness had significant differences between the normal group and mild, moderate to severe degree groups (P < 0.05), and had no differences between the mild and moderate to severe degree groups (P > 0.05). If 1.25, 0.65, 1.05, 0.55 cm were used as the critical value of the fatty renal capsule thickness for ultrasonic diagnosis of fatty liver at the long axis inferior pole, short axis surround of right kidney and left kidney, the sensitivities were 72.7%, 75.0%, 72.7% and 77.3% respectively, the specificities were 93.7%, 87.5%, 93.7% and 87.5% respectively. CONCLUSION: The fatty renal capsule thickness can be used as the reference index for the ultrasonic diagnosis of fatty liver disease.