The present study aims at investigating the correlations between the expatriate manager's adaptability and performance by using the method of survey on the expatriate manager of Taiwanese, Japanese, and US Subsidiaries in Thailand. A total of 700 questionnaires were sent to the managers of the subsidiaries run by the Taiwanese, Japanese, and US MNEs in Thailand. Totally 385 questionnaires were returned. After removing 117 invalid questionnaires, there were 268 valid questionnaires. The response rate was 55%. According to the results of the study, a positive correlation between the expatriate manager's adaptability to different cultures and their performance was found. In the American MNEs, the expatriate manager's adaptability produced a significant effect on their performance.