Objectives: Traditional treatment methods are becoming popular and commonly used in many societies and have become the first treatment option for most people. While some of these methods are helpful, they can interact with medications the patient is taking for another disease and cause a variety of life-threatening risks. Valerian (catweed) plant is used in traditional medicine as a sleep aid due to its sedative effects. Valerian may also exert anticancer effect Materials and Methods: In this study, the cytotoxicty and oxidative stress effects of valerian root extract were evaluated in human liver hepatocellular carcinoma (Hepg2) and human colorectal adenocarcinoma (Caco2) cell lines. The cytotoxicity was evaluated via the 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide test. Total reactive oxygen species analysis was performed via a 2',7'-dichlorodihydrofluorescein diacetate assay in flow cytometry. Results: Inhibition concentration 50 values were calculated as 936.6 and 1097.5 µg/mL in the Hepg2 and Caco2 cell lines, respectively. It was observed that valerian root extract did not induce oxidative stress in HepG2 and Caco2 cell lines. Conclusion: These results indicate that the use of valerian root extract as an alternative method in cancer treatment may not be effective and may cause a risk for public health. On the other hand, it may be safe at recommended tolerated concentrations since it does not cause oxidative stress.