Objectives: To investigate the in vitro cytotoxic, phytotoxic, and insecticidal activity of Chrysophthalmum montanum (DC.) Boiss. Materials and Methods: The crude methanol (80%) extract of the aerial parts of C. montanum was fractionated to obtain n-hexane, chloroform, n-butanol, and remaining water fractions. The crude extract and subsequent solvent fractions of the plant were evaluated for their biological activities using screening bioassays such as cytotoxicity on brine shrimp lethality, phytotoxicity against Lemna minor L., and insecticidal activity against Rhyzopertha dominica and Tribolium castaneum. Results: The cytotoxicity assay revealed that the crude extract, n-hexane, and chloroform fractions of the plant had positive lethality with LD 50 values of 71.51, 126.62, and 75.95 µg/mL, respectively. The extract and its fractions, except for the remaining water fraction, showed phytotoxic activity, which was expressed as percentage growth regulation in a concentration-dependent manner. n-hexane and chloroform fractions in particular had 100% growth inhibition (GI) at 1000 µg/mL, followed by the n-butanol fraction (62.6% GI) and crude extract (40.0% GI) of the plant at the same concentration. Otherwise, all samples had no insecticidal activity against R. dominica and T. castaneum. Conclusion: This study demonstrates that C. montanum contains bioactive compounds related to potential biological activities such as cytotoxic and phytotoxic.