The stratigraphical relation between the Karatsu and Sasebo coal-fields has been discussed by many geologists, but opinions diverge concerning the boundary between the Kishima (Ashiya) and Sasebo (Ainoura formation) groups., Detail observations on the said boundary, especially on the lower parts of the latter and the top of the former groups in the Karatsu coal-field, led the writers to review Ueji's classification of the Ainoura formation, and to add supplementary notes to previously published reports on the Kishima group., The newly proposed boundary between the Sasebo and Kishima groups is based upon the following stratigraphical data: (1) Marked differences in lithology between the coal-bearing formation of the Sasebo group above, and the "flysch" type Hatazu shale comprising the top of the Kishima group below., (2) The Kishima group is missing in the northeast of the Karatsu coal-field, where the redefined Sasebo group directly overlies the Pre-Tertiary basement complex (granites)., The Hatazu shale is separated from the overlying thin basal conglomerate (ca., 1 m thick) of the Sasebo by an erosion surface., The conglomerate contains angular boulders having lithological characters identical with the underlying strata., From such evidence, the writers conclude that tilting of the area towards the northeast may have begun as early as the beginning of deposition of the Sasebo group in the northern extremity (present day Higashimatsura Peninsula) of the Karatsu coal-field., On the other hand, crustal movement caused a shift in the position of the Kishima basin near the end of the Kishima (Ashiya) age, as already stated elsewhere., (3) Although the geological age of the Sasebo and Kishima groups have long been believed by most Japanese geologists to be Oligocene, the writers hold the view that the Paleogene-Neogene break should be defined by the Kishima-Sasebo boundary., This view is upheld by the above-mentioned evidences supplemented by paleontological data., However, the writers admit that further paleontological data is necessary to settle the problem., It is expected that future paleontological investigations will favour this assumption.,