Flavonoids have an ability to suppress various ion channels. We determined whether one of flavonoids, cyanidin-3-glucoside, affects adenosine 5'-triphosphate (ATP)-induced calcium signaling using digital imaging methods for intracellular free Ca2＋ concentration ([Ca2＋]i), reactive oxygen species (ROS) and mitochondrial membrane potential in PC12 cells. Treatment with ATP (100μM) for 90 sec induced [Ca2＋]i increases in PC12 cells. Pretreatment with cyanidin-3-glucoside (1μg/ml to 100μg/ml) for 30 min inhibited the ATP-induced [Ca2＋]i increases in a concentration-dependent manner (IC50=15.3μg/ml). Pretreatment with cyanidin-3-glucoside (15μg/ml) for 30 min significantly inhibited the ATP-induced [Ca2＋]i responses following removal of extracellular Ca2＋ or depletion of intracellular [Ca2＋]i stores. Cyanidin-3-glucoside also significantly inhibited the relatively specific P2X2 receptor agonist 2-MeSATP-induced [Ca2＋]i responses. Cyanidin-3-glucoside significantly inhibited the thapsigargin or ATP-induced store-operated calcium entry. Cyanidin-3-glucoside significantly inhibited the ATP-induced [Ca2＋]i responses in the presence of nimodipine and ω-conotoxin. Cyanidin-3- glucoside also significantly inhibited KCl (50 mM)-induced [Ca2＋]i increases. Cyanidin-3-glucoside significantly inhibited ATP-induced mitochondrial depolarization. The intracellular Ca2＋ chelator BAPTA-AM or the mitochondrial Ca2＋ uniporter inhibitor RU360 blocked the ATP-induced mito-chondrial depolarization in the presence of cyanidin-3-glucoside. Cyanidin-3-glucoside blocked ATP- induced formation of ROS. BAPTA-AM further decreased the formation of ROS in the presence of cyanidin-3-glucoside. All these results suggest that cyanidin-3-glucoside inhibits ATP-induced calcium signaling in PC12 cells by inhibiting multiple pathways which are the influx of extracellular Ca2＋ through the nimodipine and ω-conotoxin-sensitive and -insensitive pathways and the release of Ca2＋ from intracellular stores. In addition, cyanidin-3-glucoside inhibits ATP-induced formation of ROS by inhibiting Ca2＋-induced mitochondrial depolarization.