In a survey of microfungi from plant debris collected in Vietnam, two new hyphomycetous species were found, which belong to the genera Heliocephala and Pseudopenidiella and the family Microthyriaceae ( Microthyriales, Dothideomycetes). Maximum Likelihood and Bayesian Inference sequence analyses of the internal transcribed spacers (ITS) and large subunit (LSU) of the ribosomal DNA barcodes allowed assessing the phylogenetic relationships of the new species with other species of the respective genera. Heliocephala variabilis sp. nov. was closely related to Heliocephala elegans, Heliocephala gracilis, and Heliocephala zimbabweensis, from which it was morphologically distinguished by its smaller conidiophores and non-rostrate conidia of up to four septa on the natural substratum. Pseudopenidiella vietnamensis sp. nov. was related to Pseudopenidiella piceae and Pseudopenidiella podocarpi and differed from the former principally by its lack of microcondiophores and from P. podocarpi by having larger macroconidiophores and smooth conidia. Key morphological features to distinguish the accepted species in Heliocephala and Pseudopenidiella are also provided. In addition, Pseudopenidiella pini was excluded from the genus on the basis of its morphological features.