The apostille route applies to South Korea
Because both South Korea and China are parties to the Hague Apostille Convention, a document issued in South Korea does not go to a Chinese embassy or consulate. It is certified once, in South Korea, and mainland China accepts that certificate directly.
The Convention has operated between South Korea and mainland China since 7 November 2023, the date it entered into force for China. South Korea was already a party before then.
In South Korea the apostille is issued by: either the Ministry of Foreign Affairs or the Ministry of Justice, depending on the document. Confirm the current competent authority on the HCCH listing linked below before travelling anywhere — designations change, and several countries split the work between more than one body.
Korea designates four authorities in all. For a diploma the relevant two are the Ministry of Foreign Affairs, which handles administrative documents, and the Ministry of Justice, which handles notarial acts and official certificates placed on privately signed documents. Which applies depends on how your document was issued, so ask before queueing at either.
What this does not cover
Certification only proves the signature and seal are genuine. It does not translate the document and it does not oblige any university to accept it. Language requirements are set separately by whoever receives the document, so confirm those first, and have any translation made after certification so the certificate is included in it.
Frequently asked questions
Do documents from South Korea need an apostille for China?
Yes. South Korea and mainland China are both parties to the Hague Apostille Convention, so a document issued in South Korea needs an apostille from the competent authority there, and does not need to be taken to a Chinese embassy or consulate.