The Confuciusornis avifauna, Sinosauropteryx fauna, pterosaurs, conchostracans, insects, bivalves and plants (including fossil woods) of the Yixianian Stage are ascribed to the late Late Jurassic or Late Tithonian; the mammalia, dinosaurs of ornithischia and sporopollens to the early Early Cretaceous or the Berriasian Stage; and the ostracods and fishes to the transition from Late Jurassic to Early Cretaceous or the Late Tithonian-Berriasian. Considering that the Yixianian biota may be compared or correlated with the Solnhofen biota of Germany, the Purbeck biota in England, Late Jurassic Terori-type and Ryoseki-type floras in Japan and that they are also related to the Middle Jurassic Yorkshire flora and the Great Estuarine conchostracans fauna, the synthetic age of the Yixianian Stage may be determined as Late Tithonian to Berriasian, and the ages of the Jianshangou Bed and the Dakangbu Bed tend to be the Late Tithonian and the Berriasian, respectively. Because the Jurassic-Cretaceous boundary of the Purbeck Group (Formation or Bed) that may be roughly correlated with the Yixianian Formation is not yet affirmed, and as there lack measured data, the 144 Ma, 145 Ma or 135 Ma data for the Jurassic-Cretaceous boundary ages recommended by the International Stratigraphical time table cannot be used as a reliable criterion. Therefore, the establishment of the Jurassic-Cretaceous boundary should be based on the synthetic biological age and measured isotope age of the Yixianian stratotypes in China. Accordingly, the boundary age is preferred to set between the Jianshangou Bed of the lower Yixianian Stage and the Dakangbu Bed of the upper Yixianian Stage, and the isotope age of 124 Ma is preferably chosen because it conforms the synthetic biological age at present.