The Cairo-Jeddah route topped with 3.23 million seats, according to aviation analysis firm OAG, which assesses the world's most competitive routes based on the number of seats reserved.
Cairo-Riyadh ranked third on the list followed by Bangkok-Seoul and Antalya-Moscow.
Nine carriers operate 1,733 flights between Da Nang and Seoul from October 2021 to September 2022, according to OAG's data.
Da Nang has long been a favorite tourist destination for South Koreans.
In 2019, the year before the pandemic broke out, it received 1.7 million visitors from South Korea.
Vietnam has allowed free-quarantine entry since March 15 and resumed visa exemption for South Koreans.
South Korea reopened its borders to foreign tourists in June.