Abstract: Electron-microprobe Th-U-Pb chemical age determination of monazite is a new in-situ geochronological method developed over the last few years.Its basic permises are that monazite contains a negligible amount of common lead and that the Th／U／Pb values are not affected by any processes excepting Th and U radioactive decay.Therefore,Th-U-total Pb chemical age of monazite Can be obtained by high-precision determination of mother and daughter elements and statistical analysis.Using the intemational standards of Th02,U metal,PbCrO4 and YAG as standards,we carried out systematic evaluation of experimental conditions and analyses for Th-U-total Pb chemical dating of monazite on a JEOL JXA-8 100 electron microprobe .Application of this electron-microprobe chemical dating of monazite from a metasedimentary rock of the Jingangkou formation,Wutai Group,Wutai Mountains yielded three distinct isochron ages:2 172±37 Ma(n=4),1 922±24 Ma (n=40), and 1 847±62 Ma(n=6).The 2 172 ± 37 Ma age.in agreement with SHRIMP U-Pb zircon ages for granitoid magnmtism in the Wutai group, appears to represent an early thermotectonic event.The 1 922±24 Ma age is within the analytical uncertainty of the metamorphic age of 1 911±38 Ma, detemfined by an internal Sm-Nd isochron of whole-rock and metamorphic minerals.Also, the 1 847 ±62 Ma age is similar to the 1 850 Ma SHRIMP metamorphic zircon ages in neighbouring Hen~han and Fuping complexes.These geologically significant results from the Wutai Group indicate that this electron-microprobe Th-U-total Pb chemical dating of monazite has obvious advantages over other geochronological methods.