The medicinal mushroom Chaga, Inonotus obliquus (Pers.:Fr.) Pilát (Hymenochaetaceae), has been used in folk medicine in Russia, Poland, and most of the Baltic countries, as a cleansing and disinfecting measure, and as decoctions for stomach diseases, intestinal worms, liver and heart ailments, and cancer treatment. Many reports have been published concerning the health promoting functions of this mushroom, including antibacterial, hepatoprotective, anti-inflammatory, antitumor, and antioxidant activities. The purpose of the present study was evaluation of in vitro anticancer activity of fraction IO4 isolated from I. obliquus. The effect on cell proliferation, motility and viability was assessed in a range of cancer and normal cells. Chaga fraction prepared from dried fruiting bodies was subjected to anticancer evaluation in human lung carcinoma (A549), colon adenocarcinoma (HT-29), and rat glioma (C6) cell cultures. Human skin fibroblasts (HSF), bovine aorta endothelial cells (BAEC), models of rat oligodendrocytes (OLN-93), hepatocytes (Fao), rat astroglia, and mouse neurons (P19) were applied to test toxicity in normal cells. The following methods were applied: tumor cell proliferation (MTT assay and BrdU assay), cytotoxicity (LDH assay), tumor cell motility (wound assay), tumor cell morphology (May-Grünwald-Giemsa staining), and death detection (ELISA). Chaga fraction elicited anticancer effects which were attributed to decreased tumor cell proliferation, motility and morphological changes induction. Of note is the fact that it produced no or low toxicity in tested normal cells. The data presented could open interesting paths for further investigations of fraction IO4 as a potential anticancer agent.