Aim. To study the significance of cyclin-dependent kinases (Cdks) in paclitaxel-dependent apoptosis in colon and undifferentiated thyroid cancer cells. Materials and Methods. Experiments were performed on undifferentiated thyroid carcinoma (KTC-2) and colon carcinoma (ARO) cell lines. Cells were treated with paclitaxel (Ptx) and inhibitor of Cdk, roscovitine. Cell survival test and Western blotting were used for characterization of the effects of paclitaxel and roscovitine on cancer cells. Results. It was shown that not c-Jun N-terminal kinase, but cyclin-dependent kinases are responsible for antiapoptotic Bcl-2 phosphorylation. Cdk inhibition enhanced the cytotoxic effects of Ptx at low drug concentrations. There was antagonism between Ptx and roscovitine at higher (25 nM) paclitaxel concentrations. Conclusion. Using of paclitaxel at low (2.5 to 5 nM) concentrations and roscovitine is a promising combination for further preclinical trials for the development of new therapeutic approaches to the treatment of colon and anaplastic thyroid cancer.