When learning a foreign language, it is important to learn how to spell accurately as it is crucial for communication. To spell Thai language accurately is challenging for both native and foreign learners of Thai. However, studies that address spelling errors made by foreign learners of Thai are rare. The purpose of this paper is to analyze patterns and causes behind spelling errors made by Chinese students learning Thai as a foreign language. Data was taken from thirty Chinese students who took part in a Thai language composition writing and dictation task. The results suggest that the main spelling problem for Chinese students is spelling Thai vowels (37.5%), followed by initial consonants (20.7%), final consonants (20.4%), unpronounced letters (18.0%), tone markers (2.2%), and others (1.2%). In terms of underlying causes of spelling errors,
irregularities in Thai language and interference from Chinese phonology are the two main causes for their spelling errors. Moreover, carelessness, differences between the Chinese and Thai writing systems, and influence from Thai native speakers also account for some of the spelling errors produced among the Chinese students.