The UV-Vis spectra, HRTEM and AFM images of cationic fullerene derivative 1 with ammonium head group directly connected to C60 skeleton in tetrahydrofuran (THF)-water (H2O) binary mixtures and in pure H2O were investigated. It was found that the UV-Vis spectra of ammo-nium 1 in the THF-H2O mixtures with THF% ≥ 20% were nearly overlapped, while those with THF% < 20% showed broadened and red-shifted peaks, indicating the formation of aggregates. Corresponding to the UV-Vis spectral changes, the solvatochromism of ammonium 1 in THF-H2O mixtures was observed. Ammonium 1 in binary THF-H2O mixtures existing as the monomer state could aggregate upon pro-longed standing. Higher temperature and lower concentra-tion speeded up the aggregation process. The UV-Vis spectra, HRTEM and AFM images of cationic fullerene derivative 1 with ammonium head group directly connected to C60 skeleton in tetrahydrofuran (THF) -water (H2O) binary mixtures and in pure H2O were investigated. It was found that the UV- Vis spectra of ammo-nium 1 in the THF-H2O mixtures with THF%> 20% were nearly overlapped, while those with THF% <20% showed broadened and red-shifted peaks, indicating the formation of aggregates. Corresponding to the UV- Vis spectral changes, the solvatochromism of ammonium 1 in THF-H2O mixtures was observed. Ammonium 1 in binary THF-H2O mixtures existing as the monomer state could aggregate upon pro- longed standing. Higher temperature and lower concentra- tion speeded up the aggregation process .