Korea Customs Allowances information

Korea Customs Service : http://www.customs.go.kr 

A written baggage declaration must be submitted to a Customs officer upon entry.
Passengers must clear Customs through either the green, white, or red channel. Passengers who have no articles to declare should use the green channel. If a passenger declares non-duty-free articles voluntarily, the declared amount will be accepted and the clearance procedure will be expedited.  

Duty-Free Articles
• Visitors' (non-residents) goods which will be taken out of Korea upon departure. (The total quantity of the goods should be declared for duty exemption).
• Goods which were declared upon departure from Korea and are being brought back.
• 1 bottle (not over 1 liter) of alcoholic beverages and 200 cigarettes (50 cigars or 250 grams of tobacco)
• 2 ounces of perfume
• For further information on goods subject to declaration and prohibited goods, please contact the Customs Information Office at Incheon International Airport. 

Guidelines for Currency Regulation
Passengers entering Korea who are carrying foreign or Korean currency valued at over USD 10,000 must declare it to a Customs official. Departing non-residents of Korea who are carrying foreign or Korean currency (including traveler's or bank checks) valuing more than USD 10,000 must obtain permission from the bank of Korea or Customs, not including any amount carried into Korea and declared on arrival, which may be carried out without declaration to Customs. Residents of Korea must declare any currency or negotiable checks more than USD 10,000 upon departure.
Please be aware that violators of these regulations are liable to be fined and/or otherwise penalized under the Foreign Exchange Transactions Act.  

[sources : visitkorea.or.kr]