Geochronology of Cenozoic basalts from Inner Mongolia have been systematically studied by means of K一Ar dating,where there were 14 samples from Chifeng district, 15 from Jining and 21 from Abaga. MM1200B static vacuum mass spectrometer was used for K一AI dating,The measuring errors 0f both 40Ar and 36Ar Were all 0.1-0.05% and 36Ar 1-5%and age error 5－10％（1σ). The results show the evolution of Cenozoic basalts in the area. At first,the basalt eruption started from both Chifeng and Jin- ing districts in 33一28 Ma of Oligocene, and then from southeast to northwest it gradually extended to the southern basalt plateau and the northern basalt plateau in Abaga in turn.It reached cli- max in 11一10 Ma of Middle Miocene, Both Chifeng and Jining districts became dormant in 9-7 Ma of Upper Miocene, and the n， about 4 Ma of Pliocene, the eruption of the northern basalt p1- ateau in Abaga ended up,while the southern basalt plateau did not end-off until 0,33 Ma of Pleistocene. In addition, we have found out about the ages ranging f rom Pliocene to Pleistocene in southern basalt plateau in Abaga, whi- ch may be useful for study of the age of the Quaternary-Ter- tiary boundary.