Two diketopiperazine derivatives, altenarizines A (1) and B (2), and a new glucosyl sesterterpene, 24-a-Dglucosyl-()-terpestacin (3), together with two known phytotoxic sesterterpenes, ()-terpestacin (4) and fusaproliferin (5), were isolated from the fermentation broth of an endophytic fungus Alternaria alternata, which was obtained from the fresh root of Ceratostigma griffithii. Structures of all the isolates were identified by spectroscopic data.