The inhibition to nucleation and growth of urinary crystal calcium oxalate (CaOxa) crystallization and the stabilization to calcium oxalate dihydrate (COD) by an aqueous extract from Tiankui soup, a Chinese traditional medicine from Tujiazu, were studied by scanning electron microscopy (SEM) and X-ray diffration (XRD). When the amount of Tiankui was less than 30 mg/mL, only calcium oxalate monohydrate (COM) crystals were grown. When the amount of Tiankui was 45 and 75 mg/mL, COD crystals were induced, and the percentage of COD was 95% and 100%, respectively. The extract from Tiankui can stabilize the existence of COD crystals. In pure water, COD transformed to COM crystals in 48 h, while only 20% of the COD was transformed in the presence of 12 mg/mL of Tiankui. These chemical basis about the inhibition to CaOxa growth and about the induction and stabilization to COD crystals were explained in terms of the active constituents of the extract, the adsorption difference of the constituents with calcium oxalate crystals, and the coordination of the constituents with Ca²⁺ ions.

Key words: calcium oxalate, crystallization, urinary stone, Chinese medicine