Several Bipolaris and Curvularia spp. were collected from different disease symptoms of Poaceae in Thailand. Phylogenetic analyses based on DNA sequence data of the internal transcribed spacer region and intervening 5.8S nrRNA gene, and partial fragments of the glyceraldehyde-3-phosphate dehydrogenase and the translation elongation factor 1-α genes, demonstrated that these isolates represent one new species of Bipolaris, B. brachiariae, and five new species of Curvularia, i.e. C. chiangmaiensis, C. dactyloctenicola, C. nodosa, C. pseudobrachyspora, and C. variabilis. Bipolaris brachiariae is related to B. heliconiae, B. maydis, and B. saccharicola, but produces shorter conidiophores and conidia. Curvularia chiangmaiensis is characterized by very long conidiophores to 2 mm. Curvularia dactyloctenicola is closely related to C. chiangmaiensis, but can easily be distinguished by the size of its conidiophores and conidia. Curvularia nodosa is related to C. hawaiiensis and C. dactyloctenii, but it produces abundantly knotted hyphae, which were not observed in the other two species, as well as shorter conidia with fewer septa. Curvularia pseudobrachyspora is related to C. brachyspora, but differs in the size of its conidiophores. Finally, Curvularia variabilis can be easily distinguished by its highly variable conidia. Furthermore, the description of B. oryzae is emended to include two isolates belonging to this species from Thailand that produce much longer conidiophores and conidia with fewer septa than observed in previous descriptions. The present study is also the first report of Bipolaris bicolor, B. setariae and B. yamadae from Thailand. Moreover, new hosts are reported for B. bicolor (Eleusine indica), B. setariae (Imperata cylindrica), and Curvularia verruculosa (Eleusine indica).