Sixty one of the marine macroalgal species (39 genera) were collected and identified from three coasts: Derna, Susa and Tolmeta;which lie to the eastern of the Libyan coast. Twenty one species of these algae (34.43%) belonged to 13 genera of Chlorophyta, Twenty species of them (32.79%) belonged to 9 genera of the Phaeophyta, and twenty species (32.79%) belonged to 17 genera of the Rhodophyta; with a clear dominance of Cystoseira species. The relatively richest coast was Susa which has 38 algal species. Tolmeta coast comes at the second rank with 33 algal species while the poorest one was Derna coast with 12 species only (none of them belonged to Phaeophyta). The ecological status of marine surface waters and its purity could be arranged according to the species enrichment index of these coasts as follows: Susa > Tolmeta > Derna. The three coasts shared together only three green species and one red species (Hypnea musciformis). The similarity indices were 24% and 26.67% between Derna coast and both of Susa and Tolmeta, respectively. Meanwhile, the highest similarity value was (57.14%) between Susa and Tolmeta coasts.