ABSTRACT. – The present paper reports the results of a study on macroalgal epiphytic assemblages of the Mediterranean seagrass Posidonia oceanica. The floristic composition was determined and patterns of spatial variability of epiphytic assemblages were analysed at several spatial scales, from regional level (hundreds of kilometers) to patch level (meters), using morphological groups as descriptors. A total of 77 macroalgal species was identified, among them 7 Chlorophyta, 11 Ochrophyta and 59 Rhodophyta. The most common species identified are characteristics of this assemblage, while few species seem to be quite rare: Bryopsis penicillum, Cottoniella fila - mentosa var. algeriensis and Spermothamnion strictum. In all the meadows studied, epiphytic assemblage was dominated by crustose forms; filamentous algae were widely distributed with low abundances, while foliose and corticated terete species showed generally low covers and were absent in some meadows. Both multivariate and univariate analyses applied to the abundance of morphological forms showed as significant the variability at the largest and the smallest scales investigated, among Meadows and Quadrats respectively, while the intermediate scales resulted not significant. However, large-scale variability was due only to two meadows that showed a low percentage cover of epiphytes, while the structure of the assemblages and the species composition appeared similar through all the other meadows. These results suggested that epiphyte assemblages of P. oceanica leaves are homogeneous at large-scale, but highly variable at small scale, indicating a patch distribution of the organisms inside the meadows.