Betulin and oleanolic acids (pentacyclic triterpenoid secondary metabolites) have broad pharmacological activities and can be potentially used for the development of anti-cancer and anti-AIDS drugs.In this study, we detected the accumulation and the distribution characteristics of betulin and oleanolic acid in various organs of white birch at different ages.We also determined the expression of 40SC genes (LUS, β-AS, CAS1 and CAS2) involved in the triterpenoid synthesis pathways by real time RT-PCR.The result showed that the 1-year old birch can synthesizebetulin and oleanolic acid.In addition, betulin and oleanolic acids were mainly distributed in the bark, while the content in the root skin and leaf was very low.The content of betulin and oleanolic acid in birch varied in different seasons.The content of betulin and oleanolic acid and their corresponding LUS and β-AS geneexpression were very low in 1-year old birch.With increasing age of birch, betulin content was increased, while oleanolic acid was decreased.Similar changes were also observed for their corresponding synthesis genes LUS and β-AS.In the leaf of 1-year old plant, the highest expression of CAS1 and CAS2 occurred at end of September, while expression of L US and the β-AS was low from June to October.In the stem skin, high expression ofβ-AS and the LUS genes occurred from the end of July to September.In the root, high expression of the β-AS gene was observed at the end of October.These results indicated that triterpenoid gene expression was similar to the triterpene accumulation.Expression of LUS gene and β-AS gene in birch with different ages were corresponding to the betulinic and oleanolic acid accumulation.Expression of CAS1 and CAS2 genes were elevated with increasing age of birch.This study provides molecular mechanisms of triterpenes synthesis in birch plants.