The Caoshan and Jiguanshi intrusions composed of pyroxene dioritic porphyrite and granodiorite are exposed in the Shizishan orefield, Tongling, Anhui Province, eastern China. Based on new petrographic observations and microprobe analyses of pyroxene and hornblende megacrysts and cumulates from the intrusions, in combination with mineral crystallization temperature and pressure calculations, the authors found some evidence for the Mesozoic mantle-derived magma underplating in this area. The petrographic and mineralogical data presented in this paper suggest the existence of alkali-olivine basalt magma underplating before 140 Ma± in this area. The formation of the pyroxene megacrysts and the hornblende megacrysts as well as cumulates resulted from crystallization differentiation of intermediate-basic magma in the deep magma chamber at the depths of 28 km to 33 km through the assimilation of the underplated alkaline basaltic magma with the lower sima crust. The formation of the pyroxene cumulates resulted from the crystallization differentiation of intermediate magmain the shallow magma chamber at the depths of 19 km to 21 km, through the assimilation of the intermediate_basic magma with the epimetamorphic rocks.