We reported the studies of aggregation, cellular uptake and cytotoxicity of C(60)(OH)(x), one of important water-soluble fullerene derivatives. The results showed C(60)(OH)(x) was smaller in size but harder to go into cells in the media with serum. Moreover, C(60)(OH)(x) showed severe toxicity to Chinese hamster lung and Chinese hamster ovary cells, but almost no effect on L929 cells, which implied that the cytotoxicity of C(60)(OH)(x) was cell type specific. Flow cytometry was used to examine the precise effect of C(60)(OH)(x) on the cell cycle and found cells was blocked at G1 phase. These results are expected to be helpful to understand the toxicity of fullerene derivatives.