Hydrogen has a significant protective effect on calcium oxalate-induced renal injury, but its effect on metabolic profiles is unknown. This study showed the effects of hydrogen on serum and urine metabolites in a renal injury model. Ultra-HPLC quadrupole time-of-flight-MS-based metabolomics was used to characterise metabolic variations. Twenty-five serum metabolites and 14 urine metabolites showed differences in the the nitrogen and oxygen inhalation (NO), nitrogen and oxygen inhalation combined with calcium oxalate induction (CaOx), and hydrogen inhalation combined with calcium oxalate induction (HO CaOx) groups. Nineteen serum metabolites and 7 urine metabolites showed significant restoration to normal levels after hydrogen gas (H 2) treatment. These metabolites are primarily related to amino acid metabolism, fatty acid metabolism, and phospholipid metabolism. This study showed that a comprehensive metabolomics approach is an effective strategy to elucidate the mechanisms underlying the effects of hydrogen treatment on calcium oxalate-induced renal injury. Key words calcium oxalate-induced renal injury; hydrogen; metabolomics Metabolic analysis is an important component of systems biology and has been defined as "qualitative and quantitative measurement of the dynamic multiparametric metabolic response of living systems to pathophysiological stimuli or genetic modification". 1) Metabonomics analyses have been used to identify small-molecule metabolites in serum or urine for holistic metabolic profiling of the metabolic status, which can help elucidate the biological network of metabolites in normal or pathological models and can provide information on disease processes and gene function. Calcium crystals could trigger kidney injury by the following steps: firstly, transient non-adhesive contact between crystals and cells would lead to tubular epithelial dedifferentiation, secondly, the crystals may adhere to the dedifferentiated epithelium, thirdly, the accumulation of crystals would obstruct renal tubular and increase mechanical pressure, finally, the tubular epithelial gets injured by the mechanical pressure and dedifferentiation. 2) According to our previous study, inhalation of hydrogen gas (H 2) can ameliorate calcium oxalate deposition and renal oxidative stress in mice. 3) Thus, in this study, metabolic analysis of serum was performed to investigate changes in the metabolic regulatory networks in a model of renal injury induced by crystallisation of calcium oxalate. Furthermore, the effects of inhalation of high-dose hydrogen gas were assessed. Our results helped identify potential biomarkers of renal injury induced by crystallisation of calcium oxalate and analyse the potential targets of hydrogen gas.