More than 70% of the Earth’s surface is covered by seas and oceans. Their microorganism resources are abundant and partly comprise fungi, actinomycete, bacteria, and so on. These natural resources have only recently been explored for natural products; many of them are biologically active and potentially useful (Bugni and Ireland 2004; Bhakuni and Rawat 2005). Marine organisms live in high salt, high pressure, low temperature, and hypoxia, which are different environments compared with those of terrestrial organisms; hence, marine organisms form a number of secondary metabolites unique in structure (Menna et al. 2011). Alkaloids are a group of naturally occurring, nitrogen-containing, biologically active heterocyclic compounds. In addition to carbon, hydrogen, and nitrogen, alkaloids may also contain oxygen, sulfur, and, more rarely, other elements such as chlorine, bromine, and phosphorus (Knölker 2011). During the last few years, a large number of biologically important alkaloids with antiviral, antibacterial, anti-inammatory, antibiotic, antioxidant, antitumor, anticancer, and cytotoxic activities have been isolated from marine sources (Kumar and Rawat 2011). More specically, marine-derived fungi from the marine environment have shown great potential as suggested by the diversity of secondary metabolites. In recent years, numerous marine-derived fungi have been identied, and from them a variety of novel alkaloid compounds have been isolated. In general, more than 1200 new compounds have been isolated and identied from the broth of marine fungi, and they have shown different bioactivity. This chapter summarizes the development of alkaloids isolated from marine fungi, which includes indole, quinazoline, pyridoacridine, diketopiperazine, diterpenes, triazole, dihydroimidazole, and pyrrole alkaloids. These compounds are interesting areas of research for their potential anticancer and antitumor bioactivity.