A primitive sawfly, Madygella humioi sp. nov., belonging to the family Xyelidae (Hymenoptera: Symphyta), is newly described from the Upper Triassic Mine Group, Yamaguchi Prefecture, southwest Japan. The new species differs from the five previously known Madygella species in having a cell length of 1r plus 2r shorter than that of 3r + 4r and a cell height of 3r + 4r lower than 2r plus pterostigma in a forewing. To date, this is the oldest fossil record of sawflies in East Asia. Regarding genus Madygella, this is the first example found outside of the Kyrgyz Republic. This discovery provides an insight into the early evolution of the order Hymenoptera and suggests a widespread distribution of the pioneering genus Madygella during the Triassic period.