Brine shrimp assay-guided fractionation and isolation of the EtOAc soluble fraction of Phryma leptostachya L. (Phrymacaceae) gave two active compounds, phrymarolin II (1) and ursolic acid (2), which were identified by physicochemical and spectroscopic methods. Compound 1 exhibited potent lethality with $LD_{50}$ value of 0.0013 $mu extrm{g}$/ml, whereas 2 showed moderate lethality with $LD_{50}$ value of 27.0 $mu extrm{g}$/ml against brine shrimp. The cytotoxic activities of 1 and 2 were also evaluated against one murine and five human cancer cell lines employing the sulforhodamin B (SRB) method. Compound 2 exhibited cytotoxic activity against L1210 and SK-MEL-2 cells with $ED_{50}$ values of 3.70 and 9.27 mg/ml, respectively, whereas 1 was devoid of any cytotoxic activity against all cancer cells tested.