Two new species of oribatid mites of the genus Mainothrus (Oribatida, Trhypochthoniidae)—M. paratransaltaicus sp. nov. and M. davidmarshalli sp. nov.—are described on the basis of adult specimens sampled from Russia and Brunei (first record of the genus in the Oriental region). Supplementary description (SEM micrographs) for Mainothrus badius (Berlese, 1905) is presented. A revised generic diagnosis and an identification key to known species of Mainothrus are provided.