Apobaetis insolitus n. sp., Apobaetis kallawaya n. sp. and Apobaetis niger n. sp. (Ephemeroptera: Baetidae) are described fromnymphs collected in Argentina and Bolivia. Apobaetis insolitus can be distinguished by the labrum with anterior margin with aU-shaped emargination, segment II of labial palpi with triangular apically rounded distomedial projection. Apobaetis kallawayacan be distinguished by segment II of labial palpi with triangular, slender and apically pointed distomedial projection, the posteriormargins of the abdominal terga with blunt spines and paraprocts with blunt spines apically. Apobaetis niger can be distinguishedby the anterior margin of labrum with medial lobe and segment II of labial palpi with triangular apically rounded distomedialprojection. The three new species possess tarsal claws with two rows of denticles. A key to all species known fromnymphs is presented.