Two dredged samples from near ocean-continent transition zone in the northern margin of Nansha micro-block (SCS) are mainly intermediate-acid intrusive rocks representing continental basement, i.e., granodiorite (intermediate end-member) and monzonite granite (acidic end-member). This paper analyzed mineral composition (including feldspar, biotite and hornblede) of four representative rock samples by using electron microprobe technique. Mineral chemical characteristics and calculated value of temperatures and pressures support the petrogenetic model which has been supposed based on whole-rock geochemistry.