The use of medicinal plants is still of great importance as an alternative treatment method in neurodegenerative diseases, cardiovascular patients and cancer. Taraxacum officinale plant is one of the medical plants used in the treatment of many diseases as diuretic, hypolipidemic and antidiabetic thanks to the active components it contains. In order to examine the effect of Taraxacum officinal on proliferation and apoptosis in cancer, in our study, we determined the chemical composition of the Taraxacum officinal plant by gas chromatography-mass spectrometry (GC-MS) and its antioxidant status using a commercial kit. Additionally, we determined the anti-cancer effect of water, methanol and chloroform extracts of the Taraxacum officinal plant on A549 and HT-29 cancer cell lines with the help of the MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) method. Finally, we aimed to determine the relationship between the chloroform extract of the Taraxacum officinal plant, which has the highest anti-cancer properties, and apoptosis by determining the expressions of BAX, BCL-2 and Caspase-3, which are among the genes associated with apoptosis, in A549 and HT-29 cancer cell lines, with the help of Real-time Polymerase Chain Reaction (RT-PCR) analysis. We determined that the Taraxacum officinal plant has an anti-cancer effect by increasing caspase-3 expressions in A549 lung cancer cell lines and by increasing caspase-3 and BAX expressions and decreasing BCL-2 expression in HT-29 colon cancer cell lines. In light of the data we obtained, we can say that the Taraxacum officinal plant has anti-cancer properties that cause a decrease in cell proliferation by regulating the expression of genes related to apoptosis