The effect of urinary pH value on the composition of urinary nanocrystals was investigated by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy.The differentiation of composition of urinary nanocrystals not only occurred between the people with different urinary pH,but also occurred in the same person when his or her urinary pH changed.At lower urinary pH (such as pH＜5.8),most of the urinary components are uric acid,acidic phosphate,calcium oxalate etc.However,most of these components are urate,phosphate,magnesium ammonium phosphate,calcium oxalate etc at higher urinary pH (such as pH＞6.2).Combining XRD and FTIR methods,the compositions of urinary nanocrystals can be determined accurately.It is helpful to exploring the cause of urinary stones.