Abstract: In order to ascertain the hydrocarbon source strata age of Xiushui basin, LA-ICP-MS zircon U-Pb dating was conducted on the sub-volcanic rocks that was emplaced in the third member of Yixian Formation sedimentary strata in Xiu-D1 well and developed on the surface, which yielded an age of 121.5±1.2~121.3±3.5 Ma, indicating that the sub-volcanic rocks were formed in Early Cretaceous.In comparison with the volcanic rocks in the surrounding areas, the study of isotopic chronology shows that the volcanic rocks in Xiushui basin were formed during the volcanic activity at the end of the formation of Yixian Formation.The determination of the age defines not only the upper age limit(121.3 Ma)of the formation of volcanic rocks but also the upper age limit(121 Ma)of the main hydrocarbon source rocks(the third member of Yixian Formation)in Xiushui basin.The third member of Yixian Formation is an important oil and gas exploration target series in northwest Liaoning Province.It provides a new target series for oil and gas exploration in the peripheral fault basin group of Songliao basin.