Human immunodeficiency virus type 1 protease (HIV-1 protease) is essential for replication of HIV-1 and has been identified as a potential target for AIDS. During the course of screening for HIV-1 protease inhibitors, Mer-N5075A was discovered in the culture filtrate of a soil-isolated Streptomyces and turned out to belong to the MAPI group of compounds (Fig. 1). In this paper, we report the production, isolation, structure determination of Mer-N5075A, and its biological activities.