Ethyl acetate fraction column chromatographic analysis was used to isolate eleven compounds (numerically tagged 1–10) from Cassia occidentalis L. in this study. Two unique metabolites, including a neolignan compound designated as occidentalignan I (9) and a 4avonoidal glycoside, chrysin-7-O-)-L-rhamnopyranosyl (10), were identi8ed, while silybin A (8) was the 8rst 4avonolignan to be isolated from the Fabaceae family. Four compounds, including *-sitosterol-3-O-*-D-glucopyranoside (1), stigmasterol-3-O-*-D-glucopyranoside (2), betulinic acid (3), and vanillic acid (4) were isolated from C. occidentalis for the 8rst time. In addition, four known compounds, cinnamic acid (5), p-hydroxybenzoic acid (6), *- resorcylic acid (7), and citric acid (11),
were also detected. )e in-vitro cytotoxicity assessment of the methanolic extract of C. occidentalis on seven cancer cell lines, including A-549, Colo-205, Huh-7, HCT-116, PANC-1, SKOV-3, and BNL, demonstrated its selective potent cytotoxicity on lung cancer cells without aCecting normal BNL cells. In contrast, the methanolic extract showed moderate activity on Colo-205 and Huh-7 and nearly no activity on HCT-116, PANC-1, and SKOV-3 cell lines. )ese results suggest that the methanolic extract of C. occidentalis is an excellent candidate with potential antiproliferative activity against lung cancer; however, further studies are necessary to clarify its mechanism of action.