Large amounts of Mesozoic magmatic rocks are exposed in the coastal area of the southeastern China. The data of geochemistry and zircon U-Pb ages of granitoids from typical plutons in the coastal area of Zhejiang and Fujian are studied systematically in order to explore the reason for the complexity of magmatism during the period of 100~90 Ma. Methods:Comparative analyses of regional geochemical characteristics, U-Pb zircon geochronology and Rhyolite-MELTS method to calculate magma processes at 100~90 Ma in Zhejiang—Fujian area. Results: Plagioclase is as the main mineral in Zhejiang—Fujian plutons at 98 Ma, while typical minerals of aegirine and large amounts of perthitic feldspar appear at 95 Ma and 92 Ma respectively. The Late Mesozoic high alkaline granites in Zhejiang—Fujian area are different from those typical island arc granites in the world. They are enriched in LILE, depleted in HFSE Nb-Ta, and Ba and Sr, strong Eu anomalies and varied LREE/HREE ratios. Most of them during this period are derived from partial melting of continental crust materials and existing the transition in chemical composition at 95 Ma. Conclusions:The parental magma of Zhejiang—Fujian Late Mesozoic granites during the period of 100~90 Ma are derived from partial melting of the mantle materials caused by the subduction of the paleo-Pacific plate. Magmatic evolution in Zhejiang—Fujian area showed a magmatic transition due to the intervention of mantle materials at 95 Ma, and the transition period of the granitic formation in Zhejiang—Fujian area is probably about 95 Ma.