In these days the base of non-profit domestic corporation is very important problems in corporate tax act. Non-profit domestic corporation shall mean a domestic corporation which falls under any of the following : (a) Corporation established under Article 32 of the Civil Act, (b) Corporation established under the Private School Act or other special Acts whose purpose is similar to that as prescribed in Article 32 of the Civil Act (excluding any corporation other than a partnership corporation as prescribed by the Presidential Decree, which is capable of paying dividends to stockholders, employees or investors), and (c) Unincorporated organization which is treated as a corporation under Article 13 (4) of the Framework Act on National Taxes (hereinafter, an "organization treated as a corporation"). The corporate tax act is a statute that provides the regulatory details of corporate taxes which are assessed on the earnings and liquidation incomes of a corporation for each fiscal year. A person who is liable to pay a corporate tax shall be a domestic corporation, and a foreign corporation shall be liable to pay it only where it has any withholding income in Korea. The business year of a corporation shall be one accounting period prescribed by Acts and subordinate statutes or the corporation-s articles of incorporation, which shall not exceed one year. The tax base for corporate tax on the income for each business year of a foreign corporation with a domestic place of business, a foreign corporation with income from domestic real estates or real estate rights, or a foreign corporation with forestry income shall be the total amount of income generated from sources in Korea minus the amount of losses generated during the five business years immediately preceding the current business year, non-taxable income, and income generated by the navigation of a ship or aircraft to a foreign country, which are deducted in sequential order. The income of a corporation for each business year shall be the total amount of losses incurred during the business year deducted from the total amount of earnings during the business year. In this case, earnings shall mean the amount of proceeds generated by transactions which increase the net assets of the concerned corporation, and losses shall mean the amount of losses generated by transactions which cause a reduction in the net assets of the concerned corporation. This Act provides the objects of and standards for non-inclusion in the calculation of earnings and losses: to be concrete, proceeds from capital transactions, marginal profits from the evaluation of assets, dividend amounts received by a holding company, dividend amounts received from an equity investment in another corporation, etc. shall not be included in the calculation of earnings, and marginal losses from the evaluation of assets, depreciation costs, donations, entertainment expenses, excessive expenses, non-business expenses, interest on loans, etc. shall not be included in the calculation of losses, for both of which the detailed standards are prescribed in this Act. Reserve funds for proper business purposes, liability reserve funds under Acts, a policyholder dividend reserve funds for an insurer to pay dividend to insurance policyholders, the allowances for severance and retirement benefits, bad debt allowances to cover bad debts, etc. shall be included in the calculation of losses, for which the detailed requirements are prescribed in this Act. In this paper I wrote about base of non-profit domestic corporation in corporate tax act ; Income of profit-making business of non-profit domestic corporations, Separate Accounting (where a non-profit corporation operates a profit-making business, the assets, liabilities, and profits and losses of the concerned profit-making business and the other business that is not a profit-making business must be separately accounted for and separate accounts must be maintained), Inclusion of reserve funds for proper purpose business in deductible expenses.