Developing an effective conservation plan for endangered sea turtles requires the comprehension of their distribution, habitat use, and migration routes. Various methods such as mark and recapture, satellite telemetry, and genetic research have been employed to figure out their movement. However, there are certain limitations, such as low returns, high costs, and limited resolution, to investigate sea turtles that cover wide areas of habitats and have long diving durations. As an additional method, the use of epibiotic barnacles can be considered. The shells of commensal barnacles residing on sea turtles provide an isotopic history that reflects the temperature and salinity of the seawater that the host has encountered. In this study, the chronological isotopic history on the shell surface of commensal barnacles was measured by utilizing secondary ion mass spectrometry (SIMS). Isotopic values (δ18Ocalcite and δ¹³Ccalcite) were obtained in certain intervals, from commensal barnacles attached to four sea turtles stranded on Jeju Island, Republic of Korea: 2 loggerhead turtles (Caretta caretta), 1 green (Chelonia mydas), and 1 hawksbill (Eretmochelys imbricata). δ18Ocalcite was used to estimate the locations of the turtles using balanomorph barnacle paleotemperature equation (BBPE), and δ¹³Ccalcite was used to estimate the influence of salinity to increase the accuracy of the isoscape. One loggerhead turtle displayed a meandering trajectory, wandering between the Philippines, Taiwan, and the Ryukyu Islands, and the other loggerhead turtle took a direct route from the eastern part of the Philippines to Jeju Island. The green turtle predominantly remained in the vicinity of Jeju Island, while the hawksbill turtle undertook a northward journey from south of Jeju Island. This study is an attempt to study sea turtle migration routes in East Asia by analyzing commensal barnacles using SIMS.