Disclosed are: a marker for the diagnosis of a liver disease, which can determine the disease in a simple manner; an antibody directed against the marker; a diagnostic agent; a diagnosis method; and a method for marker detection in blood or serum. Proteome analysis revealed that quantities of the full-length kininogen and three partial peptides thereof (sequence A: position-440 to position-456, sequence B: position-439 to position-456, and sequence C: position-438 to position-456) in sera of patients with non-alcoholic fatty liver disease are significantly different from those in sera of healthy individuals; and a diagnostic agent and a detecting method for the non-alcoholic fatty liver disease that can be conveniently used for medical examination are established. The use of a combination of a kininogen-based marker and a C4-based marker (the full length sequence or partial peptides thereof) enables identification of chronic hepatitis and an asymptomatic virus carrier, as well as non-alcoholic fatty liver disease.