The Wangzhoushan caldera is located in Cangnan County, southern Zhejiang Province, and the main eruption products are Late Cretaceous rhyolites and rhyolitic pyroclastic rocks. The central intrusive in the caldera is the typical alkaline granite, containing typical alkaline ferromagnesian minerals arfvedsonite and aegirine with micrographic texture and miarolitic structure. LA-ICP-MS zircon U-Pb dating results show that the formation ages of alkaline granite are 91.3±1.1~90.4±0.8 Ma. The alkaline granites have high SiO2 contents (76.9%~77.9%), and alkalis contents (Na2O+K2O=7.80%~8.51%), and low CaO, MgO, Al2O3. They are rich in large ionic lithophile elements (LILE; e.g., K, Rb, Th, U) and high field strength elements (HFSE; e.g., Nb, Ta, Zr, Hf), poor in Ba, Sr, P, Ti, and show high (Ga/Al) × 104 ratios (3.82~4.28) and high zircon saturation temperature (798~889 ℃). Different samples of the Wangzhoushan alkaline granite have similar whole-rock Nd isotopic compositions (εNd(t)= -4.2~-3.8) and zircon Hf isotopic compositions (εHf(t)= -6.4~-1.7), indicating that the Wangzhoushan alkaline granite may be mainly derived by partial melting of crustal materials with minor contributions from mantle-derived components. The Wangzhoushan alkaline granite belongs to the typical peralkaline A-type granite, which is another example found in the Late Mesozoic A-type granite belt in the coastal areas of Zhejiang and Fujian Provinces. The magma origin of the Wangzhoushan alkaline granite and the contemporaneous coastal alkaline granite (101~86 Ma) in Zhejiang-Fujian is controlled by the subduction and rollback of the paleo-Pacific plate in the Late Cretaceous. Under the strong extensional tectonic setting, the depleted mantle-derived magma upwelled, resulting in the partial melting of the middle and lower crustal materials, and the magma of the high-silica peralkaline A-type granite was formed by the magma mixing and fractional crystallization processes.