The ascomycetous families, Didymosphaeriaceae and Montagnulaceae, have been treated in Pleosporales, Dothideomycetes, and both include saprobes, endophytes and pathogens associated with a wide variety of substrates worldwide. Didymosphaeriaceae was characterized by 1-septate ascospores and trabeculate pseudoparaphyses, mainly anastomosing above the asci, while species in Montagnulaceae had 1 to multi-septate ascospores and generally cellular pseudoparaphyses. In recent treatments, Bimuria, Didymocrea, Kalmusia, Karstenula, Montagnula, Paraphaeosphaeria, Paraconiothyrium and Letendraea were placed in Montagnulaceae, while only Didymosphaeria has been placed in Didymosphaeriaceae. New morphological and molecular data from recent collections have become available and thus the understanding of the families can be improved. Based on analyses of concatenated internal transcribed spacer (ITS) with LSU, SSU and beta-tubulin gene sequences, the taxonomy of the genera classified in these families are re-assessed. Our phylogenetic analyses conclude that, the recently introduced Didymosphaeria rubi-ulmifolii with Paraconiothyrium brasiliense species complex, Alloconiothyrium, Bimuria, Deniquelata, Didymocrea, Kalmusia, Karstenula, Letendraea, Montagnula, Neokalmusia, Paraconiothyrium, Paraphaeosphaeria, Phaeodothis and Tremateia, forms a robust clade named here Didymosphaeriaceae. We therefore synonymize Montagnulaceae under Didymosphaeriaceae which is the oldest name and has priority and provide a update account of the family. Didymosphaeria is represented by Didymosphaeria rubi-ulmifolii. A new genus, Neokalmusia, is introduced in the family to accommodate the bambusicolous taxa Kalmusia brevispora and K. scabrispora. This introduction is based on molecular data coupled with morphology. One new species, Paraconiothyrium magnoliae and the sexual morph of Paraconiothyrium fuckelii, is also introduced. Julella and Barria are assigned to the family based on morphological similarity with Didymosphaeriaceae. Wilmia (previously referred to the Phaeosphaeriaceae) is synonymized under Letendraea (Didymosphaeriaceae). Furthermore, a new species, Letendraea cordylinicola, is introduced and placed in Didymosphaeriaceae based on phylogeny and morphology. The paraphyletic nature of Paraconiothyrium is partially resolved, but further sampling with fresh collections and molecular data of species in this genus are needed to obtain a natural classification.