Outbreaks of oyster diseases caused by the World Organization for Animal Health (OIE)-listed protozoan pathogens have been a global concern for several decades. With the wide application of species-specific and sensitive polymerase chain reaction (PCR) techniques, it is now well known that even the Pacific oyster, insusceptible to Perkinsus marinus, Bonamia ostreae, Bonamia exitiosa could act as a carrier host. Furthermore, one of the transmission pathways of oyster pathogens includes anthropogenic activities, such as the discharge of ballast water or hull attachment during international maritime shipping. In this survey, OIE-listed pathogens, including B. ostreae, B. exitiosa, and Marteilia refringens were screened in the Pacific oysters growing in small bays off the south coast of Korea using PCR with OIE-recommended species- or genus-specific (Bonamia) primers. The survey sampled 1980 oysters from 35 sites in small bays in the south, where more than 95% of the national productions are yielded. The PCR screening indicated that none of the oysters screened in this study were positive for B. ostreae, B. exitiosa, P. marinus, and M. refringens. This study first investigated the OIE-listed protozoan pathogens in the Pacific oysters culturing in Korea, and the results indicated that the Pacific oysters raised on the south coast of Korea are free from those OIE-listed pathogens. For secure and sustainable oyster farming on the south coast, however, regular monitoring of such invasive oyster pathogens is recommended, as the international maritime trade activities are increasing in Korea.