The objective of this thesis is to analyze the pattern of interdependence between in the fire insurance business and the automobile insurance business. This research is divided into group of small companies and group of large companies, each of which is classified by sum insured of fire insurance and automobile insurance. Cross section data of 60 fire insurance companies and 56 automobile insurance companies in 1995 is used to compare with 1996. Econometric model of general least square method is used for such empirical test. It is found that there is no conjectural variations between firms in the fire insurance business which is proved to be the business in the oligopolistic industry, both within and across each size group, the same result is also found with the automobile insurance business.