To evaluate the nutritional status according to the degree of metabolic acidosis(MA) and determine that MA is a risk factor for malnutrition, we screened the laboratory data of 37 hemodialysis(HD) patients who were clinically stable for more than 6 months and taken bioelectrical impedence analysis(BIA) twice 6 months apart to check lean body mass (LBM). Mean age of patients was 49.1+/-15.0 years and sex ratio 1:2.4. Mean serum albumin level was 3.97+/-0.36g/dl and weekly Kt/V and normalized protein catabolic rate(nPCR) were 3.04+/-0.85 and 0.99+/-0.21g/kg/day. According to mean total CO2 content during the periods between BIA, the patients were divided to three groups[group 1(n=16):&18mEq/L, group 2(n=9):18< or =tCO2&21mEq/L, group 3(n=12):> or =21mEq/L). Group 1 had significantly higher body weight gain than group 2 and 3(1.82+/-1.62 vs. 0.77+/-3.13 and 1.35+/-3.85kg, P<0.05), and higher LBM gain(1.99+/-4.38 vs. 3.35+/-7.99kg, P<0.05), nPCR(1.05+/-0.20 vs. 0.91+/-0.13g/kg/day, P<0.05), intact parathyroid hormone(88.4+/-78.7 vs. 32.0+/-26.5pg/ml, P< 0.05), and phosphate(5.4+/-1.3 vs. 3.9+/-1.3mg/dl, P< 0.05) than group 3. There were no differences in age, serum albumin, BUN, creatinine and weekly Kt/V among three groups. Mean total CO2 level was inversely correlated with body weight gain and LBM gain. In conclusion, metabolic acidosis in stable HD patients may be the result of high protein intake and not related to decrease of body weight by protein catabolism.