Notch (N) is a cell surface receptor that mediates an evolutionarily ancient signaling pathway to control an extraordinarily broad spectrum of cell fates and developmental processes. To gain insights into the functions of N signaling in the adult brain, we examined the involvement of N in Drosophila olfactory learning and memory. Long-term memory (LTM) was disrupted by blocking N signaling in conditional mutants or by acutely induced expression of a dominant-negative N transgene. In contrast, neither learning nor early memory were affected. Furthermore, induced overexpression of a wild-type (normal) N transgene specifically enhanced LTM formation. These experiments demonstrate that N signaling contributes to LTM formation in the Drosophila adult brain.