In the course of surveys on dothideomycetous fungal genera associated with various hosts in Taiwan, Neomassaria-like species were collected as saprobes on dead stems of Rhododendron sp. Maximum likelihood and Bayesian phylogenetic analyses based on concatenated LSU, rpb2, SSU and tef1 gene matrices indicate that Neomassaria-like isolates generated in our study formed a separate clade in a sister group relationship with Neomassaria fabacearum with high statistical support. Hence, the new species Neomassaria formosana is described to accommodate the new linage in Neomassaria. The new species is characterised by immersed to erumpent, papillate ascomata with a dark brown peridium, fissitunicate, cylindrical to oblong asci and fusoid to ellipsoid, hyaline, bicellular ascospores with 4–6 large guttules. Moreover, Neomassaria formed a monophyletic and well-supported lineage with an uncertain phylogenetic placement within the Pleosporales. Therefore, the new family Neomassariaceae is proposed for the genus Neomassaria within the order Pleosporales, Dothideomycetes. The morphological characters also support justification for both the new family and the new species.