Nothofagus is regarded as a key group for interpreting Southern Pacific biogeographical history.Based on a molecular phylogenetic tree, a quantitative dispersal-vicariance analysis (DIVA) of the genus is presented. The results indicate that the ancestral area of Nothofagus is a broad realm almost including the total extant distribution pattern of the genus rather than a so-named center of origin. Integrated with the paleogeography, the time of origin and subsequent diversification is inferred to have started in the Late Cretaceous. Most vicariance and dispersal events should be contained in that period. Vicariance events versus dispersal events play a dominant rule in speciation. The dispersal events are hypothesized to hap-pen from the Late Cretaceous to Eocene in terms of the geological history. Rich fossils are collected in the Eocene. South America, comprising three subgenera of Nothofagus, should be considered as a diversifi-cation region, in which the distribution of the species of subgenus Fuscospora and subgenus Nothofagus are explained by dispersal events during the Late Cretaceous-Late Eocene.