Acute myeloid leukemia (AML) is a clonal, neoplastic disease characterized by abnormal proliferation of myeloid progenitor cells. Genetic and epigenetic changes in AML patients impair proliferation and differentiation of myeloid progenitor cells. TET2 functions in DNA demethylation and mutations are frequently observed in patients with AML. Caffeic acid phenethyl ester (CAPE) is an active com- ponent of propolis, a resinous substance collected by honey bees from various plant sources. CAPE’s antioxidant, anti-inflammatory, antiviral, immunostimulant and anticancer effects have been shown in various studies. In this study, we aimed to investigate CAPE’s effect on TET2 mRNA expression. In K562 cell line, TET2 mRNA expression upon CAPE treatment was controlled with qRT-PCR. To decrease TET2 mRNA expression commercially available TET2 mRNA targeting shRNAs and a control shRNA were used. Transfec - tion grade plasmids were then used to transfect K562 cells and antibiotic selection was applied for stable transfection. CAPE activity on cell viability in TET2 downregulated cells was assessed with Wst-1 assay. 5mM CAPE treatment increased TET2 mRNA expression fold change up to 2.5 times (p< 0.05). Two different shRNAs downregulated TET2 mRNA expression almost 50% compare to control plasmid (p< 0.05). TET2 downregulated cells were found more resistant to CAPE treatment (shRNA1; p< 0.0001 and shRNA2; p< 0.05). Our findings suggest that CAPE acts on cells by changing TET2 mRNA expression in K562 leukemia cells. In addition, TET2 downregulated cells were found more resistant to CAPE suggesting that TET2 expression may play a role in response to conventional treatments.