Two new Kirschsteiniothelia species are proposed in this study; both were collected on decaying wood from Chiang Mai and Chiang Rai provinces in northern Thailand. The taxa were isolated and the morphological characters are described and illustrated. ITS, LSU and SSU combined sequence analysis showed taxa of Kirschsteiniothelia separating into three lineages: (i) K. elaterascus grouped within Morosphaeriaceae (Pleosporales); (ii) K. maritima clustered with Mytilinidion spp. as a sister group in the Mytilinidiaceae clade; and (iii) the two new Kirschsteiniothelia species, which produce Dendryphiopsis anamorphs in culture, clustered with K. aethiops (the generic type) and the anamorph D. atra. The new family Kirschsteiniotheliaceae is introduced to accommodate taxa grouping with K. aethiops. K. elaterascus is transferred to Morosphaeria (Morosphaeriaceae) and a new genus Halokirschteiniothelia is introduced to accommodate K. maritima (Mytilinidiaceae).