The components of the fluids released from alkali basalts and mantle-derived lherzolite xenoliths in eastern China have been determined by the vacuum pyrolysis-mass spectrometric (MS) method in the present study. The results show that mantle-derived lherzolites formed in fluids composed mainly of reducing gases such as H2 and CO, and their fluid composition is characterized by a higher H2 content and a lower total content of volatiles. The fluids in alkali basalts are composed mainly of oxidizing gases, such as CO2 an SO2 and characterized by higher contents of SO2 and volatiles, implying that the extraneous oxidized fluids which are composed mainly of SO2 mixed with primary alkali basaltic magmas during their formation and evolution. The fluid compositions of alkali basalts and lherzolite xenoliths show high nonhomogeneity in the upper mantle source region and difference in alkali basaltic magma evolution in different districts. It can be deduced that the region with higher PH2 could exist in the upper mantle beneath eastern China. The components of the fluids released from alkali basalts and mantle-derived lherzolite xenoliths in eastern China have been determined by the vacuum pyrolysis-mass spectrometry (MS) method in the present study. The results show that mantle-derived lherzolites formed in of reducing gases such as H2 and CO, and their fluid composition is characterized by a higher H2 content and a lower total content of volatiles. The fluids in alkali basalts are composed mainly of oxidizing gases, such as CO2 an SO2 and characterized by higher contents of SO2 and volatiles, implying that the extraneous oxidized fluids which are composed mainly of SO2 mixed with primary alkali basaltic magmas during their formation and evolution. The fluid compositions of alkali basalts and lherzolite xenoliths show high nonhomogeneity in the upper mantle source region and difference in alkali basaltic magma evolution in different districts. It can be deduced that the region with higher PH2 could exist in the upper mantle beneath eastern china