The green tea polyphenol (−)-epigallocatechin-3-O-gallate (EGCG) has various biological activities, including anti-inflammatory, anti-neoplastic, anti- and pro-apoptotic, and neuroprotective effects. Although these are often associated with increased intracellular reactive oxygen species (ROS) and Ca2+ levels, their involvement in biological effects is poorly understood. Here we report that EGCG induces cytokine production in mast cells via Ca2+ influx and ROS generation. EGCG at concentrations of ≥50 μM induced interleukin-13 and tumor necrosis factor-α production in RBL-2H3 and bone marrow-derived mast cells. The effects were dependent on extracellular Ca2+, and EGCG induced Ca2+ release from intracellular stores and Ca2+ influx. Ca2+ influx was suppressed by 2-aminoethoxydiphenyl borate, an inhibitor of store-operated Ca2+ (SOC) channels, including Ca2+ release-activated Ca2+ channels and transient receptor potential canonical channels. EGCG failed to induce Ca2+ influx through SOC channels. EGCG-activated Ca2+ channels were genetically and pharmacologically distinct from Cav1.2 L-type Ca2+ channels, another route of Ca2+ influx into mast cells. EGCG evoked release of superoxide (O2•−) into the extracellular space. Exogenous superoxide dismutase, but not catalase, inhibited EGCG-evoked Ca2+ influx and cytokine production, indicating that extracellular O2•− regulates these events. EGCG can serve as a powerful tool for studying O2•−-regulated Ca2+ channels, which may be selectively involved in the regulation of cytokine production but have yet to be elucidated.