Mitomycln derivatives having a novel substituted dithio- ethylamlno group an 7-position. These compounds are better than mitomycin C with respect to an oncostatic activity and toxicity. Specifically, compounds showing a wider effective administration region against sarcoma 180A, a higher life prolonging effect gainst P$88, and a less marrow depressing effect are disclosed. Some of them have a high water solubitity which is advantageous in forming a pharmaceutical preparation, thus facilitating preparation of excellent oncostatic agents.