The phytochemical investigation of the dichloromethane root extract of Sesamum alatum led to the isolation of 18 compounds. Among these, compounds 3-8, defined as 9-hydroxy-2,2-dimethyl-2H-benzo[g]chromene-5,10-dione 6-O-β-d-glucopyranoside (3), (2S,3R)-3,4,7-trihydroxy-2-(3'-methylbut-2'-en-1'-yl)-2,3-dihydro-1H-inden-1-one (4), (Z)-2-(1',4'-dihydroxy-4'-methylpent-2'-en-1'-ylidene)-4,7-dihydroxy-1H-indene-1,3(2H)-dione (5), (S)-2,5,8-trihydroxy-3-(2'-hydroxy-3'-methylbut-3'-en-1'-yl)naphthalene-1,4-dione (6), 6-hydroxy-3-(3'-methylbut-2'-en-1'-yl)-4-oxo-4H-chromene-5-carboxylic acid (7), and (S)-2-(1'-hydroxy-4'-methylpent-3'-en-1'-yl)anthracene-9,10-dione (8), respectively, have not yet been described. Their structures were elucidated based on spectroscopic data analysis, including IR, NMR, HRESIMS and ECD measurements. Additional known compounds, namely, hydroxysesamone (1), anthrasesamone A (2), 2,6-dimethoxy-1,4-benzoquinone (9), syringic acid (10), syringaresinol (11), 2,3-epoxysesamone 8-O-β-d-glucopyranoside (12), 2,3-diacetylmartinoside (13), 2,3-epoxy-4,5,8-trihydroxy-2-prenyl-1-tetralone (14), ursolic acid (15), chlorosesamone (16), 2,3-epoxysesamone (17), and 2-(4-methyl-3-pentenyl)anthraquinone (18) were isolated. The antiproliferative activity of the compounds was tested against the RPMI 8226 multiple myeloma cell line. When compounds presented an IC50 value <10 μM, they were tested against two other multiple myeloma cell lines, MM.1S and MM.1R. Compound 17 was found to be the most potent, with IC50 values of 0.6, 0.7, and 0.9 μM, respectively, for the three cell lines.