In the statistical studies on the butterfly-fauna of various localities belonging to Kyushu and Chugoku District, the relation between the percentage of each element and the total number of species was introduced as shown in Fig. 1 B (P & P' : Palaearctic element in Chugoku and Kyushu, O & O' : Oriental in Chugoku and Kyushu). From the rosult it may be said that the direct comparison of the element-percentage between various districts will be unsuitable as the method for the determination of the bio-geographical situation (see Fig. 2A). The author hereby tried to use the modified e'ement-percentage, which was introduced according to the total number of species (Fig. 2B). Then he also gave the new method for the examination of bio-geographical isolation as shown in Fig.3A. In the graph, the figure, showing the deviation of element-percentage against the standard district (Kyushu), were ploed (X-axis : Palaearctic, Y-axis : Oriental). The degree of deviation was assessed by the next formula. (A-B)/B×100(%) A : Practical percentage of the element in each district. B : Theoritical percentage in a supposed district belonging to the standard region (Kyushu), where the total number of species is same as the district in question. According to the Fig. 3A, the author discussed the bio-geographical situation between Kyushu District and others, and emphasized the remarkable isolation of Nansei Is'ands against Japan proper (× Nansei Is., Kyushu D., ○ Chugoku D., □△ fr nortlern).