The ultrastructure of secretory canals in root of Angelica dahurica and the accumulation of essential oils were investigated by transmission electron microscopy (TEM) analysis.The secretion process of the essential oil was also discussed.The results indicate that the plastid,ground substances of cytoplasm and mitochondria took part in the biosynthesis of oil or oil precursor.At latter stages of development of secretory cells,numerous different sized vesicles fused with the plasmalemma and tonoplast and released the inner materia into the lumen of secretory canals.As a result,plastid and ground substances of cytoplasm were the major synthetic site of volatile oil which secreted into the lumen by diffusion or by vesicles fusing with the plasmalemma and tonoplast.Abundant mitochondria may provide energy for the series of process.