This paper aims to account for the underlying causes of spelling errors made by Thai university students.
A preponderance of Thai learners’ spelling errors is probably caused by the negative interference of the Thai writing system and the differences between the Thai and English writing systems, together with a dearth of knowledge of English phonological systems and poor lexical awareness. Awareness of the underlying causes presented in this paper may help teachers to know how to assist their students to cope with spelling in English. It seems clear that instruction in spelling has been neglected, and there is no systematic spelling instruction in English language teaching in Thailand. Arguably, incorporating this knowledge into lessons and gradually raising learners’ awareness will help in developing L2/FL learners’ orthographic abilities. In addition, it is harder for readers to understand the words used, and the message that a writer is trying to communicate might not be transmitted as intended.