The aerial parts of Gomphocarpus sinaicus Boiss. yielded four flavonoids that were identified as isorhamnetin 3-O-rhamnoglucoside (1), luteolin-7-O-glucoside-3-O-rhamnoside (2), rutin (3) and rutin-7-O-rhamnoside (4). All of the isolated flavonoids were identified by spectroscopic methods (UV, FAB-MS, $^1H-NMR;&;^{13}C-NMR$) and in comparison with the literature data. The isolated flavonoids 1, 2 and 4 are reported here for the first time from Gomphocarpus sinaicus Boiss. Three sets of experiments were carried out using the defatted alcoholic extract of Gomphocarpus sinaicus Boiss: the $1^{st}$ experiment indicated that the $LD_{50}$ was 49.82 mg/100 g b.wt. of intraperitoneally (i.p.) injected mice. The toxic signs were recorded within the first 24 hr post-injection. The $2^{nd}$ experiment revealed that the extract of the plant exhibited significant anti-inflammatory effects in normal rats. The $3^{rd}$ experiment was found that the tested doses of the extract in diabetic rats induced a significant decrease in serum glucose, AST, ALT, triglycerides, cholesterol and LDL, while HDL caused a significant increase.