Gout is arthritis induced by monosodium urate monohydrate (MSU) crystals. The treatment of gout is mainly a symptomatic treatment, by suppressing the blood uric acid concentration with drugs. Here, the changes in crystal morphology in the process of MSU crystallization were investigated. Experiments were conducted to clarify the mechanisms of nucleation and growth of the MSU crystals, revealing that MSU first precipitated as granular crystals. Thereafter, nucleation and growth of needle-like crystals were observed concomitant with the disappearance of the granular crystals. These results suggest that it is necessary to suppress the nucleation of granular crystals and the change in morphology from granular to needle-like of the MSU crystals that cause gout.