Abstract: Ziziphus spina-christi Fruits (ZSCF) have been used for human consumption for long time for medicinal purposes in many areas of the world and recommended for diseases in which free radical species are produced as a result of oxidative stress. However, there is lack of systematic study on the antioxidant capacities of ZSCF from Oman. The present study quantifies the Total Phenolic Content (TPC) and Total Flavonoid Content (TFC) and investigates the antioxidant ability of the ZSCF grown in the Sultanate of Oman. Antioxidant activity was assessed by using 2,2-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) assay (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), Superoxide-radical Scavenging Activity (SRSA), ferric reducing/antioxidant power (FRAP assay), Total Reducing Power Ability (TRPA) and metal chelation assays. Overall the ZSCF showed strong antioxidant ability and high phenolic contents. TPC and TFC contents of ZSCF were 1644 mg Gallic Acid Equivalents (GAE) and 47 mg catechin equivalents (CEQ)/100 g of Dry Weight (DW), respectively. ZSCF showed potent radical scavenging activity in each assay, showing 91% in the ABTS method (at 429 μg mL-1), 51% in the DPPH radical scavenging method (at 140 mg mL-1) and 47% of inhibition in the Superoxide-radical scavenging assay (at 20 μg mL-1). The % chelating effect of ZSCF was 94% (at 100 μg mL-1). The observed antioxidant ability of ZSCF may be due to abundant presence of phenolic contents and high electron donating ability to neutralize free radicals.