Proleptonchus aestivus and Tyleptus projectus trom Cuc Phuong natural forest are described and illustrated for the first time in Vietnam. Proleptonchus aestivus species is characterized by its body 1.14-1.21 mm long
lip region cap-like with lips amalgamated and papillae little protruding
odontostyle very slender and odontophore rod-like, arcuate
female genital system mono-prodelphic
tail short and rounded, hemispheroid. Tyleptus projectus species is characterized by its body 0.79-0.95 rom long
lip region set off by marked depression or weak constriction
six lips conspicuous projecting liplets around the oral opening
odontostyle small but robust, odontophore rod-like
female genital system mono-opisthodelphic, male genital system diorchic, with opposite testes. Tail short and rounded, to hemispheroid.