Objective  To investigate the effects of lower on-line bicarbonate concentration in dialysate to prevent metabolic alkalosis in hemodialysis (HD) patients using regional citrate anticoagulation (RCA).  Methods  The HD patients at a high risk of bleeding, having the criteria for RCA and treated in the 940th Hospital of Joint Logistics Support Force of Chinese PLA between April 2022 and August 2022 were enrolled in this study. Patients with metabolic acidosis before HD were excluded. They were then divided into two groups, conventional concentration group (dialysate bicarbonate=31.3mmol/L, n=15) and lower concentration group (dialysate bicarbonate=29.3mmol/L, n=15). The alterations of blood pH and HCO3- before and after HD were compared between the two groups.  Results  Before HD, there were no differences in clinical data, HD parameters, and levels of blood pH, HCO3- and Na+ between the two groups. In the conventional concentration group, blood pH and HCO3- were higher at the end of HD than those at the beginning of HD (7.48±0.03 vs. 7.39±0.04 and 27.50±1.93 vs. 23.57±1.13; t=6.971，5.407,P＜0.001), and 33% of the patients had metabolic alkalosis after HD. In the lower concentration group, blood pH was statistically different before and after HD (7.42±0.04 vs. 7.39±0.02, t=2.877, P=0.008), HCO3- had no difference (25.50±1.86 vs. 23.00±1.40, t=0.956，P=0.347), and no patient had the blood pH≥7.50 after HD. At the end of HD, the increased values of blood pH and HCO3- were significantly higher in the conventional concentration group than in the lower concentration group (0.07±0.02 vs. 0.04±0.03 and 4.00±1.1 vs. 1.10±0.88; t=3.223，7.756,P=0.003,＜0.001); the presence of metabolic alkalosis was significantly different between the two groups (33% vs. 0, χ2=4.375,P=0.036). The changes of blood Na+ level before and after HD had no statistical difference between the two groups (136.82±1.78 vs. 136.46±3.76 and 137.69±1.68 vs. 138.60±1.92;t=0.335、1.382，P=0.740、0.178).  Conclusions  For patients without metabolic acidosis before HD, down-regulation of bicarbonate concentration in dialysate may prevent the HD patients with RCA from metabolic alkalosis.