A facile alcoholysis of 7-methoxymitosanes and 5-methoxyindolequinone under basic conditions was discovered and a series of 7-alkoxymitosanes were synthesized from mitomycins A and B using this reaction. They showed strong antibacterial activity against various gram-positive and gram-negative bacteria and were potent inhibitors of cultivating [human cervical carcinoma] HeLa S-3 cells in vitro. Among them, 7-n-propoxy-7-demethoxymitomycin A, showed the strongest antitumor activity against solid type Sarcoma-180 in mice.