To evaluate drought stress tolerance and identifying of tolerant fennel varities/ecotypes, three synthetic fennel varieties and their seven parents in two separated experiment normal irrigation and post flowering drought stress were carried out in a complete block design with three replications in 2013 in Aburihan campus, university of Tehran, Iran. Analysis of variance showed that there was a significant difference among varities/ecotypes for all the traits in two experiments, which implies genetic variation among the fennel germplasm studied. Mean comparison showed that the highest seed yield in normal irrigation belonged to medium maturity synthetic variety and Meshkinshahr ecotype with 2357 and 2208 kg.ha^-1, respectively. In drought stress condition Meshkinshahr ecotype and medium maturity synthetic variety produced 1091 and 1081.5 kg.ha^-1, respectively. Considering drought tolerance indices, the highest mean productivity (MP), geometric mean productivity (GMP), yiled index (YI), stress tolerance index (STI) belonged to medium maturity synthetic variety, Meshkinshahr and Moghan ecotypes. Correlation coefficients between drought tolerance indices and seed yield showed that in both normal and drought stress conditions MP, GMP, YI and STI indices had positive and significant relationship with seed yield, and this implies  that selection of drought tolerant varieties are possible. In conclusion, development of synthetic varieties of fennel is recommendable and developed varieties may produce better yield in water deficit prone environments.