Fennel is one of the oldest herbs and possesses appealing flavor and beneficial medicinal effects. Fennel(Foeniculum vulgare Mill.) belongs to the Apiaceae family and its essential oil and seeds are used to flavor foods including meats, ice cream, candy, baked goods and condiments. The increasing commercial value of fennel necessitates the need to develop elite ecotypes with high essential oil content and other desired breeding and market traits. In this study fifty ecotypes of fennelfrom different part of Iran were collected and days to 70% pasty seed and essential oil content in two years and essential oil components were studied. The stage of pasty seed is the best time for essential oil extracting with the highest quantity. The results indicated that the ecotypes of Sari, Kaleibar, Qazvin, Chahestan and Haji Abad are late bearing, ecotypes of the Moqan, Kohin, Meshkin Shahr, Alamot, Khalkhal, Damavand, Ardabil, Marvdasht, Kashan, Givi, Khash and Fozve are middle bearing plants, while the remaining ecotypes were early bearing plants. As average of two year, ecotypes with the highest essential oil content (more than 3.5% per dry mater) were Razan, Fozve, Marvdasht, Kashan, Sari, Kaleibar and Arak (3.96, 3.69, 3.68, 3.66, 3.65, 3.65 and 3.54%), respectively. The GC-MASS results showed that maximum value of limonene is observed in the ecotype of Sanandaj, the maximum value of fenchone is observed in the ecotype of Sari, the maximum value of transe-anethole is seen in the ecotype of Khash and the maximum value of methyl chavicole belongs to the ecotypes of Kaleibar.