The tunicate Ecteinascidia thurstoni is a colonial sea squirt. It has a seasonal rhythm, usually present during summer months with tropical and subtropical distribution pattern. It synthesizes a group of molecules called ecteinascidines. One of which is ET-743, a compound that has a most original anti-tumoral activity and is considered today one of the most promising substances effective against various solid-type tumors (currently in the market under the commercial denomination of YondeJis for treatment of sarcoma and related tumors, or in clinical trails, phase II/1II, for other kinds of tumors). Allover the world, species of Ecteinascidia represent the only available source for this bioactive compound, which was first discovered in E, inrbinata. During the present study, the ecology of E. thurstoni along Suez Canal and Red Sea was investigated. Its populations were observed to be highly gregarious due in part to their low larval dispersal, which is very focalized, and hence, the larvae tend to settle close to their parent colonies. It is only recorded in shallow waters (0.5-1.5m) at mangrove habitats of Red Sea, epiphytic on their pneumatophores; or on pilings of jetties, and metal or cement banks of Suez Canal. Along Red Sea, a total of 29 mangrove sites were surveyed. From El-Monkata'a at Nabq Protected Marine Park (north) to Halayeb, at Egyptian-Sudanese border (south), four sites of them, namely, El-Rawisia, Wadi El Qala'an, Wadi Rawad El-Adaiah, and Wadi El-Rarada were found to have E. thurstoni. However, along Suez Canal, it is more frequent and has higher bicmass than Red Sea. It was recorded at southern sector of Suez Canal from Lake Timsah farther south to Bitter Lakes. Suez Canal's population has significantly different morphometric characteristics (zooid length, zooid weight, colony weight) than those of Red Sea. Studying the distribution of this species and locating its different populations along Suez Canal and Red Sea could help in characterizing their genetics, their chemistry and bacterial community at different isolated locations, which ultimately will help define the source of ET-743 and hence promotes its biosynthesis on commercial scale.