The nucleation, growth and aggregation of calcium oxalate(CaC 2O 4) crystals were comparatively investigated in five different mimetic systems: water, NaCl solution, artificial urine, healthy urine and lithogenic urine by using scanning electron microscopy(SEM). The effects of original concentration of calcium ion and oxalate ion and crystallization time on the morphology, density and the size of CaC 2O 4 crystals were discussed. In lithogenic urine, calcium oxalate monohydrate(COM) crystals were the dominant phase. However, a mixture of COM and calcium oxalate dihydrate(COD) with a molar ratio of about 3∶2 was obtained in the healthy urine. COD has a less affinity for renal tubule cell surface, so COD is easy to be expelled out from body and there is a less probability of stone-forming in the healthy urine. The fastest nucleation and growth of CaC 2O 4 crystals were obtained in water and NaCl solution, respectively. The size of CaC 2O 4 crystals decreases in the following order: NaCl solution>artificial urine>lithogenic urine>healthy urine>water.
