Background: Natural products display a remarkable role not only in the synthesis, design, and discovery of new drugs but also as the most prominent source of innovative drugs and bioactive substances. Genus Pulicaria (Asteraceae) includes about 100 species that are widely distributed in Europe, Asia, and Africa. Objective: In this work, the chemical investigation of Pulicaria undulata aerial parts was performed. In addition, the cytotoxic activity of the isolated metabolites was estimated toward various cell lines. Materials and Methods: Plant extract was subjected to fractionation and different column chromatography to isolate the biometabolites. Their structures were verified using nuclear magnetic resonance, infrared, ultraviolet, and high-resolution mass spectrometry, as well as compared with the literature. The cytotoxic effect was evaluated in vitro toward various cell lines: HCT-116 (colorectal adenocarcinoma), MCF-7 (human breast adenocarcinoma), and A549 (lung carcinoma). Results: A new triterpene fatty acid ester, undulaterpene A (1) (3β,16β-dihydroxylup-20 (29)-ene 3-decanoate) and four known metabolites: 3-O-acetyl-pseudotaraxasterol (2), pseudotaraxasterol (3), stigmasterol (4), and tomentosin (5) were separated. Compound 1 displayed cytotoxic potential toward hormone-dependent breast carcinoma cell line (MCF7), colon carcinoma cell line (HCT116), and lung carcinoma cell line (A549) cell lines with half maximal inhibitory concentrations (IC50s) 8.2, 6.9, and 12.4 μM, respectively in comparison to doxorubicin (IC50s 0.14, 0.39, and 1.15 μM, respectively). However, 2, 3, and 4 displayed activity toward HCT-116 with IC50s 13.2, 23.1, and 16.4 μM, respectively. Conclusion: This work led to the identification of a new triterpene fatty acid ester (1) and four known metabolites (2–5) from P. undulata growing in Saudi Arabia. The new compound showed moderate cytotoxic potential against hormone-dependent breast carcinoma cell line (MCF7), colon carcinoma cell line (HCT116), and lung carcinoma cell line (A549) cancer cell lines.