Abstract Fresh aerial parts of Tanacetum annuum L. from Morocco were steam distilled to produce an oil in 0.5% yield. The oil was fractionated on the silica gel column and analyzed by GC and GC/MS using MS and retention index data and more than 130 constituents were identified. The major components of the oil were chamazulene (38â17%), myrcene (14â1%), sabinene (8.6â4%), Î²-eudesmol (7â3%) and camphor (18â4%). Seasonal variation of the oil composition suggested that the chamazulene content decreases and the myrcene content increases from June to October.