Ephemerella quadrata, Kluge and Zhou, new species (Ephemeroptera: Ephemerellidae: Ephemerellinae) is described based on larval material from Thailand and Yunnan Province, China. The new species may be differentiated from other Ephemerellinae by its well-developed genae, smooth frons, anterior projections on the pronotum, paired anterolateral mesonotal projections, and dorsal abdominal tubercles.