Hyperoxaluria is a disorder associated with an increased risk of renal stones, one of the most common conditions. For people with hyperoxaluria, there are a limited number of effective therapeutic options. The aim of this study was to examine whether an oxalate-degrading enzyme, oxalate decarboxylase (OxdC), can inhibit crystallization of calcium oxalate (CaOx) in vitro, and whether it can prevent nephrolithiasis caused by CaOx induced by ethylene glycol (EG) in rats. When OxdC was applied at various concentrations to CaOx in vitro, there was a significant reduction in the crystallization of CaOx. The OxdC was found to inhibit crystal formation as well as the formation of crystals that had sharp edges. In animal experiments, rats that had been treated with EG showed impaired renal filtration functions, as well as increased deposition of CaOx crystals and the creation of kidney stones. It has been found that oral administration of OxdC to rats with chronic EG-induced nephrolithiasis that is characterized by CaOx intratubular crystal deposits with hyperoxaluria dramatically reduces the severity of the disease. The results of this study point to a potential therapeutic approach for treating human hyperoxaluria as well as CaOx nephrolithiasis that could be achieved by the oral administration of OxdC.