The paleomagpetic polar coordinates of Tushun basalts, infered by their paleoma}nitic data, are as follows: 1st phase of basalt; 258.1ºE, 76.8ºN(+) 2nd phase of basalt: 150ºE, 44.7ºN(一) The latter is similar to that of early Tertiary in Sibiria (152ºE, 57ºN-) and that of Early Cretaceous in Western Laioning (148.9ºE, 65ºN-).This sug- gests that the magnetic polar or Sino-Korean platy may have been only a little motion in the period of Cretaceous to Paleccene. The average isotopic age of basalt defined from 9 samples is about 64士5Ma and the K40-Ar40 isochoren age is 66.2士2Ma. Tn addition, 12 dating basalts from aialiaohe have an average K- Ar age of 71.5士8Ma. These data indicate a strong eruption of basalt and crustal tension in the period of Latest Cretaceous-Early Paleocene, which may be held as indicative of development of rift. The basalts are petrologically possessed of transitional feature between con- tinental and ocean tholeiite and belong to basalts of rift type. The basalts are saturated or lightly unsaturated with SiO2 and have FeO*/Mg0 ratio of 1.3 to 1.6, with average Ti02 content of 1.89. These rocla are increased gradually in alkalis from 1.36 in Fushun basalts to 1.63 and 1.81 in the Mesozoic basalts located in western Liaoning and Dashinganling respectively. The REE data of these rocks also demonstrated their rift nature (rich in light PEE).The crustal thickness in this area, calculated by Rb/Sr ratio (Condie 1976)，is about 30士2 kilometers which correspond completely with geophysic data. In Dashinganling, however, the thickness of crust may be up to 38-40 lcilome- ters. The fact descriptive above indicated an intensive crustal tension in this area. In summary, the eruption of basalts in Bohai-Xialiaohe-Fushun area at the time of Latest Cretaceous to Early Paleozene represented a new stage of Tancheng -L ujiang Fault developing into a rift.