Objective To examine the correlation between metabolic acidosis and malnutrition in maintenance haemodialysis (MHD) patients. Methods Forty-four MHD patients were divided into 3 groups according to plasma bicarbonate concentrations (PHCO3) and pH values. The correlation between metabolic acidosis and nutritional parameters was studied. Results The mean PHCO3 was (19.1?0.9) mmol/L in group A (n=13), (24.0?1.3) mmol/L in group B (n=22) and (27.1?0.1) mmol/L in group C (n=9). The adequacy of dialysis (Kt/V) was comparable in three groups. As compared with group B, group A had significantly higher body mass index (BMI), triceps skin fold thickness (TSF), dietary protein intake (DPI), normalized protein catabolic rate (nPCR) , Scr, serum K+ and parathyroid hormone (PTH), meanwhile, group C had significantly lower DPI, nPCR, Scr and albumin. There was no significant difference in plasma inflammatory markers C-reactive protein (CRP) among three groups. There was significant negative correlation of PHCO3 to nPCR (P