The development of new pharmaceuticals has mostly benefited from natural products. The widespread medicinal usage of species in Cleomaceae family is extensively researched. Cleome amblyocarpa Barr. and Murb. from the family Cleomaceae is a widely grown plant in Sinai Peninsula of Egypt. C. amblyocarpa is used in folk medicine as it has analgesic, anti-inflammatory, antibacterial, and antioxidant activities. in this study, the total phenolic content (TPC), total flavonoids content (TFC), and antioxidant activity of crude methanolic extract from whole parts of Cleome amblyocarpa growing in Sinai were investigated. Total phenolics and flavonoid contents of the extract were determined by the Folin–Ciocalteu and aluminum chloride methods, respectively. The total phenolic and flavonoid content of C. amblyocarpa were 15.63 ± 1.158 μg GA E/mg and 16.1 ± 0.14 µg RE/mg respectively. Two in vitro assays (FRAP, and DPPH) were used to determine the antioxidant activity and the ferric reducing ability (FRAP) by C. amblyocarpa extract was found to be (65.383 ± 3.88 μM eq/mg) in comparison with Trolox (6.414± 1.034 µg/mL). The radical scavenging activity on DPPH (IC50 values of 570.6 ± 1.045 µg/mL) was determined using Trolox as a standard drug.