In cancer research, naturally isolated 5-substituted, α,β-unsaturated lactones have become attracted the attention of scientists increasingly due to its biological activities. One of the most important member of this group of compounds is goniothalamin. Goniothalamin has high cytotoxic activity against various cancer cells and causes a minimal effect on healthy cells so it is believed that it has selective cytotoxic activity against cancer cells. In the first part of this study, anticancer activities of novel 5,6-dihydro pyran derivatives were determined by MTT assay in MCF7, PC3, HCT116 p53+/+ and p53-/- cell lines. Apoptotic effects of the selected compounds were also examined with the help of FITC labeled Annexin V-PI in flow cytometry . In the second part, anti-cancer compounds having high cytotoxic compounds were chosen and tested for their effect on cell cycle and apoptosis mechanism by flow cytometry and western blot analysis.