Withania somnifera, commonly known as "Indian ginseng" or "ashwagandha", is popular as a functional food because of its diverse purported therapeutic efficacies including invigorating, improvement of cognitive ability, and stress release activities. Chemical investigation of the MeOH extract of W. somnifera roots combined with LC/MS-based analysis resulted in the identification of six new withanolides, withasilolides A-F (1-6), as well as seven known compounds (7-13). The structures of the new compounds were established by application of spectroscopic methods, including 1D and 2D NMR, HRMS, and ECD measurements. The cytotoxicity of the isolated compounds was evaluated against four human cancer cell lines (A549, SK-OV-3, SK-MEL-2, and HCT-15). Compounds 1, 2, 4, 6, and withanone (11) each showed cytotoxicity for one or more of the four cancer cell lines used.