Betulinic acids are lupine-type pentacyclic triterpenoid saponins commonly found in some plants of Betulaceae family, especially in the bark of betula alba (birch).  The potent anti-HIV and anti-tumor activities of betulinic acids have been greatly concerned.  The natural betulinic acids include betulinic acid, 23-hydroxy betulinic acid, betulin and so on.  Some investigations on the structural modifications of betulinic acids were carried out, and many derivatives with excellent biological activity have been obtained nowadays.  In this paper, the research advances of the structural modification of betulinic acids, as well as their anti-HIV and anti-tumor activities are reviewed.