One of the factors determining drug quality in bitter fennel is the types and quantities of fatty acids stored in the seeds. We measured the fatty acid content of 50 Iranian fennel landraces. Fatty acid concentration of the 50 fennel landraces ranged from 9.5 to 23% of seed mass, and the highest amounts of fatty acid content among the early maturing races belonged to Hamedan and Arak (19.5 and 18.5%, respectively), among the medium maturing races to Marvdasht, Kohn and Meshkin Shahr (23, 20.5 and 19%, respectively), and among the late-maturing races to Sari (21%). The highest fatty acid yields belonged to Fasa (65.3 ml/m2) among the early maturing races, Meshkin Shahr and Moqhan (92.5 and 85.4 ml/m2) among the medium maturing races, and Sari (71.4 ml/m2) among the late-maturing races. The main compositions of fatty acids, measured in twelve of the landraces, were oleic acid (52-64%), linoleic acid (26-39%), palmitic acid (0.3-4.1%), stearic acid (1.3-2.4%), linolenic acid (0.6-3.6%) and myristic acid (0.35-1.07%). It was observed that landraces with high oleic acid content originated from regions with a dry and warm climate, while landraces with high linoleic acid content originated from regions with a humid and cool climate. Understanding relationships between the fatty acid profile and landrace origin climate may improve the efficiency of identifying landraces with specific fennel chemotypes. In conclusion, these results indicate that some of these fennel landraces have the potential to be complementary sources of certain fatty acids, such as oleic and linoleic acids.