The species composition and ecology of the seagrass epiphytes of Zanzibar Island (Tanzania) al-e discussed. Thalassodendron ciliatum, a subtidal seagrass species, had the highest epiphyte cover, followed by Enhalus acoroides, Halodule uninervis, Cymodocea rotundata and Thalassia hemprichii. A total of 49 taxa of macroalgae (5 of which are new records For the East African coast) was recorded as epiphytes on seagrasses; the Rhodophyta form the largest fl action, exceeding the Chloro- and Phaeophyta both in species number and abundance. The preference of the epiphytes for certain host plants was mainly related to the ecological parameters of the habitat of the hosts such as tidal level, depth and relative rate of water flow, Epiphytes were most abundant in the subtidal zone where they were best developed on the perennial stems rather than on the ephemeral leaves. Differences in species composition and abundance were also observed between different parts of the stems and leaf tufts. Distinctive species compositions characterize these different habitats and plant parts. The zonation of seagrasses and their associated epiphytes along transects through a tide channel in Chwaka Bay is also described.