Abstract The chemical composition of the volatile oils of seeds of Foeniculum vulgare Miller from two Spanish locations (Santander and Aranjuez) were investigated by means of GC and GC/MS. Leaf and stem oils of F.vulgare from Aranjuez were also examined. Two different chemotypes have been found in the seeds: (I) methyl chavicol (54.9%), fenchone (24.6%) in the seeds collected in Santander; and (II) (E)-anethole (54.9â38.1%), fenchone (22.2â34.4%) in the seeds gathered in Aranjuez. The oil from the leaves collected in Aranjuez (April, June) was found to contain methyl chavicol (12.3â12.1%), Î±-phellandrene (9.4â27.2%), limonene (25.3â18%) and fenchone (19.4â18.3%) as major constituents. The oil from the stems gathered in Aranjuez (September) was characterized by a high content of (E)-anethole (17.4â3â3%), Î±-pinene (9.7â14.4%), Î±-phellandrene (24.3â31.4%), p-cymene (11.5â5â2%), limonene (11.6â15%) and fenchone (9â1â17â5%).