Abstract: The effect of organic selenium fertilizer on contents of selenium, important trace elements and active components (saponins, flavonoids, polysaccharides and so on) of Cyclocarya paliurus (Batal.) Iljinskaja of different growth years were investigated. Three selenium spraying contents (6000, 3000 and 1500 mg/100 g) were set and sprayed in April, June and August on 10-year-old trees and 3-year-old trees, leaves were sampled respectively in May, July and September. The contents of selenium, trace elements and active components were determined. The results showed that the spraying of organic selenium fertilize could significantly enhance selenium content in leaves, and the highest selenium content of leaves could reach 7.31 mg/kg, which was 41 times as much as that of CK, the selenium content in leaves were positively correlated to the spraying amount and affected by spraying time. Leave selenium content in May was similar to that in July, and significantly higher than that in September. Leave selenium content of 10-year-old trees was higher than that of 3-year-old trees. The content of Mg, Zn, Cr, Ni, V increased after the spraying of organic selenium fertilizer, but the content of Mn and Cu decreased. The content of saponins, flavonoids and polysaccharides increased by 2.8%, 8.9% and 2.4%, respectively.