The KAr isotopic age of Mesozoic trachybasalts in western Liaoning is 84.76±1.67 Ma. Abundant ultramafic and deep crust xenoliths are found i n the trachybasalts. They consist mainly of amphibolespinellherzolite, spine llherzolite, lherzolite, plagioclasebearing amphibolewebsterite, twopyro xenegranulite and clinopyroxeneplagioclasegneiss. Study of the petrofabrics and mineral chem istry indi cate that the ultramafic xenoliths could be derived from the upper mantle and th at the granulite and gneiss xenoliths from the lower crust. The dis co very of these xenoliths is of great significance to the study of the upper mantl e and lower crust in eastern China.