The mechanisms by which leptospires caused disease are not well understood. A number of putative virulence factors have been suggested, but with few exceptions their role in pathogenesis remains unclear. In these days, many cases of leptospirosis are diagnosed by serological immunoassay. Leptospirosis is characterized by the histopathology of liver, kidney, heart, and lung, but the electrophoresis fractions of serum protein are not compared. We analyzed total protein, albumin, aspartic aminotranferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), creatinine and urea nitrogen (UN) in sera of patients diagnosed leptospirosis. Total protein and albumin were decreased in 18.5％ and 31.2％ of patients, respectively. AST, ALT, ALP, UN and creatinine were increased in 90.4％, 66.9％, 28.0％, 15.9％ and 10.8％ of patients, respectively. We performed cellulose acetate membrane electrophoresis (EP) on sera of patients increased both of AST and ALT, and of patients increased both of creatinine and UN. In patients increased both of AST and ALT, and in patients increased both of AST and ALT, the relative percentage of albumin to total protein in patient serum was dcreased in 89.1 ％ of patients. α₁-globulin, α₂-globulin, β-globulin and γ-globulin were increased in 85.1 ％, 75.2％, 33.6％ and 98.0％ of patients, respectively. In patients increased both of creatinine and UN, the relative percentage of albumin to total protein in patient serum was dcreased in 93.8％ of patients. α₁-globulin, α₂-globulin, β-globulin and γ-globulin were increased in 87.5％, 100％, 31.2％ and 93.8％ of patients, respectively. These data indicate that infection of Leptospira causes severe liver damage to most of leptospirosis patients, but doesn't cause renal damage to most of them. The relative rate of serum protein electrophoresis fractions to total protein are not identical with them of typical hepatitis patient.