Recent work on species composition, taxonomy, and diversity of plant-parasitic algae in the genus Cephaleuros in Thailand has provided additional knowledge of the parasitic algae in the country. The seven previously reported species, Cephaleuros diffusus, C. expansa, C. karstenii, C. parasiticus, C. pilosa, C. solutus, and C. virescens, are shown to cause algal leaf spot on several host plants in Thailand. Four new records are reported, namely Cephaleuros druetii, C. henningsii, C. lagerheimii, and C. tumidae-setae, resulting in a total of 11 Cephaleuros species recorded from Thailand.