The crystalline C₆₀ particles were synthesized into PDMS-based microwells on microarray chips using an ink-jet spotting system, and the effect of the particles on cytotoxicity was investigated using HeLa cells (human cervical carcinoma cell). It was found from SEM observations that a number of C₆₀ particles were formed along the edges of 300μm microwells, which could have enough area to encapsulate several tens of cells in the center. The tests with HeLa cells revealed that the C₆₀ particles irradiated green laser caused cytotoxicity, and the rate of cell death was controlled by the irradiation time. It was suggested that the cytotoxicity was induced by reactive oxygen species (ROS) generated by the C₆₀ particles, and an effect of the ROS on the cells covered a large part of the microwell.