Antioxidant capacity, flavonoid, phenolic composition in three synthetic fennel cultivars, and their elite parents were evaluated. The total range of phenols, was from 26.19 to 88.9 mg GAE/g, and total flavonoids ranged from 2.95 to 18.17 mg QE/g, and the inhibitory concentration (IC50) for free radical scavenging activity varied between 174.39 and 290.47 mu g/ml. Late maturity syn-thetic has the greatest antioxidant capacity, flavonoid, and phenolic content. The phenolic com-pounds of the fennel genotypes as determined by HPLC analysis (mg/100 g dry mass) were, sinapyl alcohol (1.756-9.034), ascorbic acid (22.11-70.00), chlorogenic acid (3.199-43.169), ferulic acid (1.081-4.413), salicylic acid (0.849-6.858), caffeic acid (1.33-6.289), coniferyl alco-hol (0.451-2.272), and p-coumaric acid (1.238-6.484). According to the principal component analysis, the first two components were responsible for 81.94% of the overall variation for phe-nol, flavonoid and, antioxidant activity. Using multivariate analysis, fennel genotypes were clas-sified into three major groups, however the synthetic cultivars showed a higher phenol content and a lower IC50 value. These findings indicated that new breeding populations are prospective sources of natural antioxidants and biochemical substances utilized in the food industry.