The cytotoxic effect of two aqueous extracts of Inonotus obliquus on human cervical uteri cancer cells (Hela S3) in vitro was evaluated. It was concluded that Inonotus extracts at a concentration of 10 micrograms/ml to 2000 micrograms/ml inhibited cancer cells growth. In cultures with extracts of the fungus a decrease of the cell proteins and mitotic index was observed. Moreover, the extracts disturbed mitoses by elevating the number of mitotic cells in metaphase. Aqueous extracts of Inonotus effected not only mitoses but also the 8/G phase of the cell cycle.