Abstract: Plant-derived triterpenoids constitute a large and structurally diverse class of natural products with various implications in industrial and pharmaceutical uses. The oleanane type triterpenoids are widely known for their pharmacological and/or biological activities. The biosynthesis pathway of oleanane triterpenoids is divided into three stages:precursor supply, skeleton synthesis, and terpenoids synthesis. Plant cytochrome P450 monooxygenases enzymes (P450s) are involved in the synthesis and diversification of natural products, and are responsible for other modifications of terpenoids, such as formation of triterpenoids. P450s-catalyzed structural modification prior to glycosylation is crucial for diversification and functionalization of triterpenoid scaffolds. In this paper, the catalyses of P450s on β-amyrin and oleanolic acid in oleanane type triterpenoid saponins biosynthesis were reviewed. Presenegenin is a major aglycon of Polygala saponins. The CYP716A249 in Polygala tenuifolia was used as an example to other P450s participating in the possible biosynthetic pathways of presenegenin. These results provide references for elucidation of the biosynthesis pathways of plant-derived oleanane type triterpenoids.