Freshwater fungi play an indispensable role in the ecosystem and have great research value. Based on morphological and phylogenetic analyses of a concatenated dataset of ITS, LSU and SSU sequences, a new species, Phaeoisaria laianensis, was introduced as a freshwater hyphomycete from Anhui Province, China. Phaeoisaria laianensis was morphologically described as erect, rigid, dark brown to black, velvety synnemata which has macronematous, septate, branched, brown to dark brown, parallel adpressed conidiophores with polyblastic, integrated, terminal, hyaline to pale brown, smooth, denticulate, sympodial conidiogenous cells and ellipsoidal to obovoid, rounded at the apex, obtuse and tapering towards base, septate, guttulate conidia. Based on molecular and morphological characteristics, it is confirmed to be a new species. All illustrations and descriptions have been provided.