Pentacyclic triterpenes have been found in many plants and can be isolated from any parts of the plant. Triterpene derivatives were shown to have biological activities including anti-HIV-1 and anti-cancer. The modes of action of the anti-HIV-1 triterpenes have been reported to be associated with virus entry, reverse transcription, virus assembly, and maturation. This review will focus on the mechanisms of action of anti-HIV triterpenes and the structural features that contribute to their anti-HIV-1 activity. Two classes of triterpenes are particularly potent and highly selective: one inhibits HIV-1 entry and the other interferes with HIV-1 maturation. Significant progresses have been made in identifying the mechanisms of action for these two classes of anti-HIV-1 triterpenes. The anti-HIV-1 entry activity is associated with a side chain at position 28 and the anti- HIV-1 maturation activity is associated with the pharmacophore at position 3. Compounds containing both of the pharmacophores at 3 and 28 positions can potently inhibit HIV-1 through their anti-HIV-1 entry and maturation activities. Although the detail mechanisms of action remains unclear, the anti-entry triterpenes target HIV-1 envelope glycoprotein, and the anti-maturation triterpenes affect the processing of the HIV-1 gag protein, CA-SP1.