The marine malacofauna, of the Pwani Province in Eastern Tanzania (Dar es Salaam, Mbudya Island) and Zanzibar Island (Nungwi) was studied in 2000. In this paper, known data from Spry (1964, 1968), Sawyer (1999, 2000) and Rosenberg et al. (2004) are supplemented by the results of the author’s fieldwork. A total of 193 gastropod and bivalve species were recorded; 39 were neither recorded by Spry (1964, 1968) nor by Sawyer (1999, 2000), of which 23 species are new for East Africa (Rosenberg et al., 2004). On the basis of the current results and the lack of a comprehensive species list, a more detailed investigation of tropical marine East African malacofauna is recommended.