This paper analyzes the changes in the elements of the accounting assumptions pertaining to the depreciation of fixed assets (depreciation unit, depreciation method and useful life), which are one of the many areas where K-IFRS and K-GAAP tend to differ. Also, this study provides the ways to improve the disclosures related to depreciation through the case analysis of D Industrial Co., LTD. The results of our analysis are as follows. First, firms have decreased the number of depreciation unit after the adoption of K-IFRS, and their depreciation methods have all changed from the accelerated depreciation method to the straight-line method. Useful life is disclosed in ranges rather than specific points, making it difficult to see the exact useful life. And overall, depreciation expenses are made to decrease by increasing the useful life of depreciable assets. Second, it is likely that managers make the decisions to decrease the depreciation expenses by increasing the useful life instead when the changes in accelerated depreciation method alone cannot decrease the depreciation expenses. Third, corporate case study shows that those with poor profitability and low financial stability are likely to decrease the depreciation expenses in order to manage their financial structures and performances at the IFRS implementation stage. Our findings suggest the needs for the Korea Accounting Institute or the Korean Institute of Certified Public Accountants to encourage firms to improve their disclosures by giving a practical disclosure guide or illustrating the best practices.