Retailers seem to be at the epicenter of the changes in intercorporate relationships and corporate behavior in Japan. But they have their own problems. The most important problem is the difficulty for retailers to sustain competitive advantage over long period. Constant adaptation to the changing environment is the key to sustaining competitive advantage. In this paper I propose the new accounting system named Dynamic Accounting for Sustainable Competitive Advantage (DASCA) to support environmental adaptation. DASCA consists of two sub-concepts : Accounting for Behavior and Duality Accounting. DASCA differs from traditional accounting designed for decision-making in three ways it uses non-accounting information it makes dual analysis and it conducts followup consistent with the hypothesis. By maintaining a dual view, accounting can describe, as faithfully as possible to reality, the multifaceted dynamism of corporate activities and help sustain competitive advantage.