It is believed that estrogen protects neurons against various toxicities like that from amyloid β (Aβ) in Alzheimer's disease (AD). In the present study, we investigated the effects of Aβ1-42 on the activities of cyclic-AMP response element-binding protein (CREB) and glycogen synthase kinase-3β (GSK-3β), two key proteins associated with learning and memory, and the effects of 17β-estradiol on Aβ(1-42)-induced changes of CREB and GSK-3β in PC12 cells. We found that Aβ1-42 induced a decrease in phosphorylation of CREB at Ser133 (CREB pS133) and caused a transient (30 min) up-regulation of the inhibitory GSK-3β phosphorylation at Ser9 (GSK-3β pS9), followed by down-regulation of GSK-3β pS9. Pretreatment of 17β-estradiol is needed for its protection against Aβ1-42-induced changes of CREB. The protective role of 17β-estradiol against Aβ(1-42)-induced down-regulation of CREB pS133 was abolished by the mitogen-activated protein kinase (MAPK) pathway inhibitor U0126. Furthermore, 17β-estradiol also prolonged the up-regulation of GSK-3β pS9 for at least 8 h. However, this action of 17β-estradiol was abrogated by PKA inhibitor H-89, AKT inhibitor LY294002, and MAPK inhibitor U0126. These results suggest that, while the protection of 17β-estradiol on CREB is MAPK dependent, its effect on GSK-3β integrates several pathways. These studies provide new insights into the role of estrogen in memory and AD.