Acidosis causes malnutrition in peritoneal dialysis (PD) patients. The effect of oral bicarbonate in PD patients with Kt/V <2.1 has not been studied. We randomly assigned 60 PD patients with acidosis and Kt/V <2.1 to oral sodium bicarbonate (0.9 g thrice daily) or placebo. Patients were followed for 12 mo. We compared their nutritional status, including subjective global assessment (SGA) score and normalized protein nitrogen appearance (NPNA), hospitalization and all-cause mortality. Treatment with oral bicarbonate resulted in a higher plasma bicarbonate level at 4 wk (27.8 +/- 2.6 versus 24.7 +/- 3.9 mmol/L, P = 0.002), and the difference persisted until 52 wk. Bicarbonate treatment had a significant effect on the change in overall SGA score (repeated measures ANOVA, P = 0.0003). The overall SGA score of the treatment group was higher than the placebo group at 24 wk (5.07 +/- 0.94 versus 4.40 +/- 1.00, P = 0.015), and the difference persisted thereafter. NPNA rose in the treatment group (1.17 +/- 0.32 to 1.28 +/- 0.26 g/kg per d, P = 0.034), but declined in placebo group (1.13 +/- 0.25 to 1.03 +/- 0.28 g/kg per d, P = 0.054). The treatment group had a shorter hospitalization than the placebo group (8.4 +/- 17.7 versus 16.8 +/- 21.7 d/yr; P = 0.02). Mortality was not significantly different. Although our trial has limited statistical power, we find that in PD patients with mild acidosis and Kt/V <2.1, oral sodium bicarbonate probably improve nutritional status and reduce the duration of hospitalization.