Rapeseed and its oil are the source of many biologically active substances. From crude rapeseed oil, canolol is isolated and from edible oil its dimer. Herein, we tested the biological activity of those two compounds isolated from the oils by determining their antioxidant capacity and in vitro cytotoxicity on human tumor cell lines. Canolol and its dimer showed antiproliferative activity on both cell lines with IC₅₀ values of 46.45 μM in HeLa, and 51.19 μM in MCF7 cells, respectively. Evaluation of cell death was also done, while the oxygen radical absorbance capacity method confirmed that the canolol dimer has higher antioxidant potential than canolol. Stability of canolol and its dimer under different storage conditions showed that for a longer period of time both compounds should be stored in a freezer, but also that the dimer is more stable against degradation than canolol. Presented results indicate possible applications of canolol and its dimer in the food and pharmaceutical industry as a natural antioxidant and an anticancer agent, respectively.