The tax law should comply with the accounting principle of substance over form. When the IRS reviews bad debts losses, “the Guidelines of Examination of Profit-seeking Enterprise Income Tax” and related “administrative explanation” are the criteria to follow. However, it should be further investigated whether the contents of them violate the principle of legal priority and cover common controversies between taxpayers and auditors. The subject of this study were the disclosed verdicts on bad debts losses. The study attempted to analyze the causes and types of the controversy of bad debts losses, the main focuses and legal basis of the court, and the influences of Article 49 of the Income Tax Act on lawsuits regarding bad debt losses. Finally, this study concluded what could be done after the amendment of the Guidelines for Examination of Profit Seeking Enterprise Income Tax Article 84 and provided some suggestions.