De acordo com Timatic você pode não precisar se você não partir para a Austrália ao chegar de Austrália.
Visa required, except for Holders of a visa issued by Australia, Canada, Japan, New Zealand or USA to nationals of Viet Nam, only if in transit through Korea (Rep.):
For details, click here
ESCLARECIMENTO
Visa Exemptions:
Holders of a visa issued by Australia, Canada, Japan, New Zealand or USA to nationals of any country except for Cuba, Iran, Macedonia (FYROM), Sudan and Syria, only if in transit through Korea (Rep.):
holding confirmed onward tickets on flights departing within 30 days; when
arriving from a third country, departing to the country that issued the visa (e.g. DEL-ICN-YVR); or
arriving on a direct flight from the country that issued the visa (a visa that expired on departure from that country is accepted), departing to a third country (e.g. YVR-ICN-DEL).
Not applicable to holders a group visa issued by Japan or an e-visa.
Not applicable if traveling from/to Guam or Northern Mariana Isl.
CLARIFICAÇÃO DO FIM
Visa required, except for A max. stay of 30 days for nationals of Viet Nam traveling as tourist, if arriving at and departing from Jeju (CJU) and For details, click here
Visa required, except for Holders of an APEC Business Travel Card (ABTC)For details, click here provided endorsed Valid for travel to KOR".
Visa required, except for Those who have previously entered Korea (Rep.) at least 4 times within the last 2 years, or at least 10 visits in total.
Additional Information:
- Nationals of Viet Nam traveling as a group on business or as a group of school children can be issued with a Group Visa.
- Holders of e-visas are required to hold an Electronic Visa Issuance Confirmation, issued by the Ministry of Justice.
- Visitors are required to hold proof of sufficient funds to cover their stay and documents required for their next destination.
Warning:
- Passport number and nationality must match those stated on the APEC Business Travel Card (ABTC).
Longa história curta você vai precisar de um visto para uma viagem: (Austrália) - > Coreia - > (Austrália) caso contrário, se você incluir o Vietnã na viagem como fonte ou como destino, poderá não precisar de visto se a partida da Coréia ocorrer dentro de 30 dias da sua chegada.