Nationals from the following countries may stay in Korea for 30 to 90 days without a visa:
Albania, Andorra, Antigua-Barbuda, Argentina, Australia, Austria, Bahamas, Barbados, Belgium, Bosnia, Brazil, Brunei, Bulgaria, Canada, Chile, Colombia, Costa Rica, Croatia, Cyprus, Czech, Denmark, Dominica, Dominican Republic, Ecuador, Egypt, El Salvador, Estonia, Fiji, Finland, France, Germany, Greece, Grenada, Guam, Guatemala, Guyana, Haiti, Honduras, Hong Kong, Hungary, Iceland, Ireland, Israel, Italy, Jamaica, Japan, Kiribati, Kuwait, Latvia, Lesotho, Liberia, Liechtenstein, Lithuania, Luxembourg, Macau, Malaysia, Malta, Marshall islands, Mauritius, Mexico, Micronesia, Monaco, Montenegro, Morocco, Nauru, Netherlands, New Caledonia, New Zealand, Nicaragua, Norway, Oman, Palau, Panama, Paraguay,Peru, Poland, Portugal, Qatar, Romania, Russia, Samoa, San Marino, Saudi Arabia, Serbia, Singapore, Slovakia, Slovenia, Solomon Islands, South Africa, Spain, St. Kitts and Nevis, St. Lucia, St. Vincent, Suriname, Swaziland, Sweden, Switzerland, Taiwan, Thailand, Trinidad-Tobago, Tunisia, Turkey, Tuvalu, UAE, United Kingdom, Uruguay, USA, Vatican, Venezuela and Yemen.
All others will need to arrange a visa ahead of time.
South Korean Visa Regulations
South Korean Embassies and Consulates