Mesenchytraeus megachaetus, new species, is described from northeast China. It is characterized by possessing enlarged ventral chaetae in segments V–VI (3–4 per bundle); nephridia with solid unlobed postseptale, relatively developed interstitial tissue and near-septal origin of the efferent duct; nephridia occurring in 5 pairs in preclitellar region; seminal vesicle absent, replaced by 5–8 naked “spermatozeugmata” in dorsal region of XI; spermathecae without diverticula and attached entally to esophagus in segment VI; atria tubular (indistinct from vasa deferentia) and without prostate glands; egg sac much developed (extending to XVII–XVIII).