We isolated the phenolic compounds epicatechin, catechin, procyanidin B-1, procyanidin B-2, hyperin and caffeic acid from the hooks and stems of Uncaria sinensis (HSUS), and studied their protective effects against glutamate-induced neuronal death in cultured rat cerebellar granule cells. Cell viability evaluated by MTT assay was significantly increased by application of epicatechin (100-300 muM). catechin (300 muM), procyanidin B-1 (30-300 muM) and procyanidin B-2 (100-300 muM) compared with exposure to glutamate only. Ca-45(2+) influx into cells induced by glutamate was also significantly inhibited by administration of epicatechin (300 muM), catechin (300 uM), procyanidin B-1 (100-300 muM) and procyanidin B-2 (100-300 muM). These results suggest that epicatechin, catechin, procyanidin B-1 and procyanidin B-2 are the active components of HSUS that protect against glutamate-induced neuronal death in cultured cerebellar granule cells by inhibition of Ca2+ influx.