Major, rare earth and trace element composition of biotites from the matrix and the intra-K-feldspar phenocrysts of granodiorite porphyry and the alteration zone in the Tongshankou Cu-Mo deposit was measured by the electron probemicro-analyzer (EPMA) and the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). EPMA analyses of major elements suggest that biotites of different modes of occurrence differ greatly in MgO and FeOT content; however, their Al2O3,TiO2,SiO2,Na2O and K2O values do not show remarkable differences. LA-ICP-MS analyses of trace elements demonstrate that biotite is an important carrier of Rb,Ba, Nb, Ta, Sc, V, Co, Ni and Cr in granodioritic melts but has less capability in hosting U, Th, Pb, Sr, Zr, Hf and Y, and thus the concentrations of these elements in biotite are much lower than those in host rocks. Post-magmatic hydrothermal process has insignificant effects on the high field strength elements such as Nb and Ta. LA-ICP-MS analyses of rare earth elements (REE) suggest that the biotites display quite low REE concentrations (∑REE=0.150×10-6～3.691×10-6), and many of the values are even lower than the detection limits. Although there are still some differences between the three types of biotites, these differences fail to accurately reflect the differentiation degree of REE during the post-magmatic hydrothermal process. So biotite is not the main mineral phase affecting the REE features of the host rocks. Geochemical features of the three types of biotites from the Tongshankou Cu-Mo deposit are similar to those of magmatic biotites: Ti=0.38～0.45 and Mg/(Mg+Fe)=0.53～0.72. Based on the geochemical features, it is suggested that the formation of Tongshankou granodiorite porphyry was related to mantle-derived magmatism and slab subduction. LA-ICP-MS analytical results of Cu in biotites from Tongshankou granodiorite porphyry are low: the highest value is only 8.442×10-6, and many of the Cu values are lower than 2.121×10-6. So the Cu content of biotites from the intrusive rocks is not an effective indicator of mineralization. High oxygen fugacity (log fO2> NiNiO+1) in the ore-forming system seems to be favorable for mineralization of porphyry copper deposits. Based on a comparison of MgO and FeO values of biotites from different types of mineralized porphyry, it is evident that biotites associated with Cu mineralization are characterized by high content of MgO and low content of FeO. On the contrary, biotites associated with Sn mineralization are characterized by high content of FeO and low content of MgO.