This article provides preliminary guidelines for researchers and investors who are interested in Korean tax law in the area of entertainments expenses via comparative analysis of tax laws in the United States and Korea. Unlike the U.S., Korea regulates entertainment expenses only by placing a ceiling on the deductible amount, not by imposing stricter conditions for a business deduction. In the U.S. 50 percent of any entertainment expense otherwise deductible is allowed. Korea places a ceiling on otherwise deductible entertainment expenses according to a mathematical formula. To determine which expenses qualify as entertainment expenses, Korean courts or administrative agencies apply a comparative analysis with other expenses. Under American tax law for a business deduction an entertainment expense at least should be associated with the active conduct of the taxpayer’s trade or business. For a business deduction a taxpayer must substantiate entertainment expenses by evidence or documents as prescribed in the relevant provisions in the U.S. and Korea.