Objective To investigate the effects of different calcium and magnesium concentration ratios in drinking water on renal lithogenesis and metabolism in rats with ethylene glycol (EG)-induced relative hyperoxaluria. Methods Normal SD rats were exposed to 0.1% EG and different Ca²⁺ and Mg²⁺ concentration ratios (360/10, 120/10, 10/10, 10/40, and 10/80, in mg/L) in drinking water for 8 weeks. After the treatments, 24 h urine volume and oxalate, citrate, Ca²⁺, and Mg²⁺ levels were measured, and the serum creatinine, blood urea nitrogen (BUN), Ca²⁺, and Mg²⁺ levels and renal pathologies were examined. Results No significant differences were found among the groups in body weight, water intake, 24 h urine volume, 24 h urinary citrate excretion, blood Ca²⁺ and Mg²⁺ levels, or serum creatinine. Ca/Mg ratios of 10/10 and 10/40 in drinking water caused a significant increase in kidney weight (P<0.05), and the latter was associated with significantly increased 24 h urinary Mg²⁺ excretion as compared with the normal control group (P<0.05). BUN was significantly higher in Ca/Mg (10/40) group than in the normal control and model groups (P<0.05). The model group and Ca/Mg groups (120/10, 10/10 and 10/40) all showed significantly increased urinary oxalate excretion compared with the normal control group (P<0.05 or 0.01); except for Ca/Mg (10/10) group, all the other treatment groups had significantly lower oxalate excretion than the model group (P<0.01). None of the groups showed detectable crystal deposition or renal pathologies. Conclusion Relative hyperoxaluria does not affect calcium and magnesium metabolism or the formation of lithogenesis and urinary calcium oxalate crystals in rats. Increased Ca²⁺ and Mg²⁺ concentrations that are below the limits in hard water can cause decreased 24 h urinary oxalate excretion. In uncomplicated hyperoxaluria, only a sufficiently high oxalate concentration can lead to lithogenesis. Urinary citrate is not affected by Ca²⁺ or Mg²⁺ ratios in drinking water.