The property changes of urinary nanocrystallites in 20 cases of uric acid (UA) stone formers after 1week of potassium citrate (K 3 cit) intake were comparatively studied by X-ray diffraction analysis, Fourier transform infrared spectroscopy, nanoparticle size analysis, and transmission electron microscopy. Before K 3 cit intake, the urinary crystallites mainly contained UA and calcium oxalate. After K 3 cit intake, the components changed to urate and UA; the qualities, species, and amounts of aggregated crystallites decreased; urine pH, citrate, and glycosaminoglycan excretions increased; and UA excretion, Zeta potential, and crystallite size decreased. The stability of crystallites followed the order: controls>patients after taking K 3 cit>patients before taking K 3 cit. Therefore, the components of urinary stones were closely related to the components of urinary crystallites.