This report provides morphological descriptions of powdery mildews found on Malvaceae, Menispermaceae, Moraceae, Nyctaginaceae, Polygonaceae, Solanaceae and Urticaceae and five specimens are identified with ITS rDNA sequences. These include a new species on Boehmeria siamensis (Urticaceae); Pseudoidium schmiedeknechtii on Schoutenia glomerata, Hibiscus floccosus and Urena lobata; E r y s i p h e k y d i a e-c a l y c i n a e o n K y d i a c a l y c i n a ; E. pseudolonicerae on Cyclea barbata; E. nyctaginacearum on Mirabilis jalapa; E. polygoni on Antigonon leptopus, Muehlenbeckia platyclada and Polygonum odoratum; Pseudoidium cf. neolycopersici on Physalis sp. and Erysiphe species on Ficus subincisa new for Thailand were described. Based on our finding, we make new taxonomic conclusions for E. nyctaginacearum, it is a new combination of Ps. nyctaginacearum found on M. jalapa and Ps. antigononis is a new synonym of E. polygoni found on A. leptopus.