Epigallocatechin gallate (EGCG), a major polyphenol of green tea, has been shown to inhibit the growth of various cancer cell lines. Co2+ is one of essential trace elements of human nutrition, both lack and excess have adverse effects on health.In this research, MTT assays were applied to investigate the effects of Co2+, EGCG and their coactions on Cal-27 cells, The results show that Co2+ and EGCG inhibited the growth of Cal-27 cells in a time-and dose-dependent model, and inhibition effects were extremely dependent on their concentrations, added orders and [Co2+]/[EGCG] ratio. Inhibitory effects of Co2+ could be decreased in the presence of EGCG. LC/MS analysis showed that a new component arised when EGCG and Co2+ were mixed together. It was inferred that the new components were [EGCG-2Co] and [EGCG-Co], and the process might be responsible for the observed effect of the bioactivities of Co2+ against Cal-27 cells.