Oribatid mite fauna of Vietnam is most studied among countries of Continental Southeast Asia but due to the brief history of detailed research, discoveries of new species are expected. Descriptions of two new species of oribatid mites (Oribatida) of the family Galumnidae—Flagellozetes (Cosmogalumna) sacculus sp. nov. and F. (C.) lineatus sp. nov.—are presented based on specimens collected from rainforest soil of Bi Dup—Nui Ba National Park (southern Vietnam). F. (C.) sacculus sp. nov. differs from other species by the presence of saccules and rare diamond-shaped granules on pteromorphs. F. (C.) lineatus sp. nov. differs from F. (C.) ekaterinae (Ermilov & Friedrich, 2016) and F. (C.) dongnaiensis (Ermilov & Anichkin, 2013) by the presence of striate pteromorph, genital and anal plates, median pore, and centrodorsal part of notogaster ornamentation represented by neural ridges band.