A new diterpene, agastanol[1] with dehydroagastol[2] was isolated from th root of Agastache rugosa, and their structures were elucidated by chemical and instrumental analysis. Agastanol[1], its derivatives, agastanone[3] and methylagastanol[5], and dehydroagastol[2] showed cytotoxic activites against in vitro human cancer cell lines. Agastanol[1] showed weak antifungal activity against Trichophyton rubrum.