The aim of this study is to review the family Behningiidae and Potamanthidae in Thailand. Two genera and three species of Behningiidae are recognised: Protobehningiamerga Peters & Gillies, 1991, Behningiabaei McCafferty & Jacobus, 2006, and Behningianujiangensis Zhou & Bisset, 2019, which is newly reported from Thailand. The egg structure of B.nujiangensis is described for the first time using scanning electron microscopy. The larva of P.merga is redescribed and its distribution is expended northward with a new record from Chiang Mai province. Two genera and five species of Potamanthidae are identified: Potamanthusformosus Eaton, 1892, Rhoenanthusmagnificus Ulmer, 1920 (new record for Thailand), Rhoenanthusobscurus Navás, 1922, Rhoenanthusdistafurcus Bae & McCafferty, 1991, and Rhoenanthusspeciosus Eaton, 1881. Our morphological evidence is supported by COI data for the family Potamanthidae. Diagnostic characters, distributions, and keys are presented for the larvae of all known species of Thai behningiid and potamanthid mayflies.