High-resolution transmission electron microscopy,X-ray diffraction,selected area electron diffraction (SAED),and energy dispersive spectroscopy (EDS) were accurately performed to analyze the components of nanocrystals in the urine of patients with calcium oxalate (CaOx) stones.XRD,SAED and FFT detected the presence of calcium oxalate monohydrate (COM),uric acid (UA),and calcium phosphate (CaP).EDS detected the elements of C,O,Ca,with a small amount of N and P.These results showed that the main components of urinary nanocrystals were COM,with a small amount UA and phosphate.HRTEM observation showed that the particle size of urinary nanocrystals was dozens of nanometers.The result was consistent with the calculation by Debye-Scherrer equation.When the urine was filtered through a microporous membrane of 0.45,1.2,and 3 μm,respectively,the number of diffraction peaks of the obtained urine crystallites increased with the increased pore size,indicating the increase of urinary crystallite species.Crystal nucleation,growth,aggregation,and adhesion of crystals to the renal epithelial cells are important processes for CaOx stone formation.The presence of a large amount of COM crystals in patients’ urine is a critical factor for CaOx stones formation.Nano UA and CaP crystallite can induce the CaOx stone formation as central nidus.