The leaves of Eucalyptus are abundant in natural resources as a novel potential antioxidant and have broad market prospect. Four of characteristic hydrolysable tannins from Eucalyptus leaves have been demonstrated great application potential as natural antioxidants in our previous research. In this study, the bioactive activities of another hydrolysable tannin isolated and identified as oenothein B (OEB) were evaluated. Content of bioactive compound (hydrolysable tannin) from different Eucalyptus species and regions in southern China were investigated. The results showed that OEB not only exerted anti-proliferative activity against HepG2 cell, but also showed higher cellular antioxidant activity than some common antioxidants. Generally, content of characteristic hydrolysable tannins decreased in the order of OEB > tellimagrandin I (T1) > pedunculagin > gemin D > pentagalloyl glucose (PGG). E. grandis × E. urophylla GL9 and E. urophylla × E. grandis could be recommended as new natural sources to exploit hydrolysable tannins because of high content, widely plantation and strong adaptability. This study supplied first insight on introduction of high cellular antioxidant activity of OEB and selecting the species and region to exploit natural antioxidants. It will promote the increasing of economic value of Eucalyptus.