Actinomycetes are a well-known source of secondary metabolites having broad ranges of biological activities such as antibiotic, anticancer and immunosuppressant. However, marine actinomycetes have been largely ignored until recently . As part of our ongoing program to develop the biomedical potential of marine microorganisms, we have focused considerable attention on the marine actinomycetes. We isolated more than 3,000 strains of marine actinomycetes from the marine samples such as deep sea and shallow water sediments, plants and invertebrates. We have established that about 10% of isolates show some bioactivity in our assays such as cytotoxicity, antifungal, antimicrobial, and enzyme inhibitory activities. From the bioactive isolates several new actinomycetes have been identified and a variety of bioactive molecules were characterized. We present here the discovery of cytotoxic compounds from marine-derived actinomycetes. The isolation, structure determination, and cytotoxicity of new compounds from marine actinomycetes will be presented.