Rhodiola rosea is a medicinal plant having stimulating and adaptogenic properties, and some reports also indicate its anticancer and antimutagenic effect. However, the mechanism of its anticancer effect is unknown as there have been no cytological studies regarding cytostatics, cell cycle, induction of apoptosis or the mitotic activity of healthy and cancerous cells. In the present paper, those parameters were investigated using HL-60 cells, with flow cytometry and fluorescence microscopy. It has been found that the extract of Rhodiola rosea rhizomes inhibits division of HL-60 cells, which is preceded by an accumulation of cells at the prophase stage. This leads to induction of apoptosis and necrosis in HL-60 cells, and to marked reduction of their survival. The cells enter apoptosis from phase G2/M of the cell cycle. After treatment with the extract, no chromosome aberrations or micronuclei were observed, which indicates the mild action of the extract. The cytostatic and antiproliferative effect of the Rhodiola rosea rhizome extract, and its mild action, raises hope for its use in anticancer therapy by enhancing the effectiveness of cytostatics.